Electronic Book

ABSTRACT

An e-book reader in which destruction of a driver circuit at the time when a flexible panel is handled is inhibited. In addition, an e-book reader having a simplified structure. A plurality of flexible display panels each including a display portion in which display control is performed by a scan line driver circuit and a signal line driver circuit, and a binding portion fastening the plurality of display panels together are included. The signal line driver circuit is provided inside the binding portion, and the scan line driver circuit is provided at the edge of the display panel in a direction perpendicular to the binding portion.

This application is a continuation of U.S. application Ser. No.15/168,674, filed on May 31, 2016 which is a continuation of U.S.application Ser. No. 14/727,113, filed on Jun. 1, 2015 (now U.S. Pat.No. 9,361,853 issued Jun. 7, 2016) which is a continuation of U.S.application Ser. No. 13/864,752, filed on Apr. 17, 2013 (now U.S. Pat.No. 9,047,799 issued Jun. 2, 2015) which is a continuation of U.S.application Ser. No. 12/769,266, filed on Apr. 28, 2010 (now U.S. Pat.No. 8,427,420 issued Apr. 23, 2013), which are all incorporated hereinby reference.

TECHNICAL FIELD

The technical field relates to an e-book reader.

BACKGROUND ART

In recent years, with the development of digitization techniques, a modehas been employed in which textual information and image information ofnewspapers, magazines, and the like are provided in the form ofelectronic data. This type of electronic data generally has a feature inwhich the content is viewed when displayed with a display deviceincluded in a personal computer or the like.

As the above display device which displays the electronic data, there isa portable display device as well as a stationary one. As a typicalexample of the portable display device, an e-book reader is given. Thee-book reader is normally provided with a display portion on its frontsurface and a page-switching key on the periphery of its main body,which is operated to display data on the next page or the previous pageon the display portion.

However, the e-book reader having the structure described above ishandled very differently from paper media such as newspapers andmagazines. An e-book reader is very different from a paper bookespecially in that pages are switched with key operation. Such adifference in the way they are handled causes the e-book reader aproblem such as a lower efficiency of text reading, sentencecomprehension, or image recognition than the paper media.

An e-book reader using a dual display device has been proposed in orderto eliminate the above difference with paper media (e.g., see PatentDocument 1 and Patent Document 2).

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2005-38608-   [Patent Document 2] Japanese Published Patent Application No.    2003-58081

DISCLOSURE OF INVENTION

It is an object of an embodiment of the disclosed invention to providean e-book reader in which destruction of a driver circuit at the timewhen a flexible panel is handled is inhibited. It is another object ofan embodiment of the disclosed invention to provide an e-book readerwhose structure is simplified.

An embodiment of the disclosed invention is an e-book reader including aplurality of flexible display panels each including a display portion inwhich display control is performed by a scan line driver circuit and asignal line driver circuit, and a binding portion fastening theplurality of display panels together, where the signal line drivercircuit is provided in the binding portion, and the scan line drivercircuit is provided at an edge of the display panel in a directionperpendicular to the binding portion.

According to the e-book reader of an embodiment of the disclosedinvention, the scan line driver circuit and the signal line drivercircuit include transistors, and the transistor included in the scanline driver circuit may have a different structure from the transistorincluded in the signal line driver circuit.

According to an e-book reader of an embodiment of the disclosedinvention, a channel layer of the transistor included in the scan linedriver circuit is formed of a non-single-crystal semiconductor, and achannel layer of the transistor included in the signal line drivercircuit is formed of a single crystal semiconductor.

According to the e-book reader of an embodiment of the disclosedinvention, the non-single-crystal semiconductor is amorphous silicon,microcrystalline silicon, polysilicon, or an oxide semiconductor.

According to the e-book reader of an embodiment of the disclosedinvention, the display portion includes a transistor, and a channellayer of the transistor included in the display portion and a channellayer of the transistor included in the scan line driver circuit areformed using the same material.

According to the e-book reader of an embodiment of the disclosedinvention, the binding portion includes any one of a battery, anantenna, a CPU, or a memory, in addition to the signal line drivercircuit.

According to the e-book reader of an embodiment of the disclosedinvention, the scan line driver circuit includes a plurality of circuitportions which are spaced from each other.

According to the e-book reader of an embodiment of the disclosedinvention, a stress concentration region is provided between theplurality of circuit portions.

According to an e-book reader of an embodiment of the disclosedinvention, the plurality of display panels includes a first displaypanel including a first display portion, a second display panelincluding a second display portion, and a third display panel which isprovided between the first display panel and the second display paneland which includes a third display portion on a first plane and a fourthdisplay portion on a second plane opposite the first plane, where thethird display panel is bent more easily than the first display panel andthe second display panel.

According to the e-book reader of an embodiment of the disclosedinvention, the first display panel includes a first photo sensorcontrolling the presence or absence of display on the first displayportion and the third display portion, the second display panel includesa second photo sensor controlling the presence or absence of display onthe second display portion and the fourth display portion, and the thirddisplay panel includes a light-shielding portion in a region overlappingwith the first photo sensor and the second photo sensor.

Further, a “semiconductor device” in this specification and the likegenerally indicates a device capable of functioning by utilizingsemiconductor characteristics, and electro-optic devices, semiconductorcircuits, and electronic appliances are all semiconductor devices.

Further, a “display device” in this specification and the like includes,in its category, a light-emitting device and a liquid crystal displaydevice. The light-emitting device includes a light-emitting element, andthe liquid crystal display device includes a liquid crystal element. Thelight-emitting element includes, in its category, an element whoseluminance is controlled by a current or a voltage, and specificallyincludes an inorganic electroluminescent (EL) element, an organic ELelement, and the like.

According to an embodiment of the disclosed invention, an e-book readerin which destruction of a driver circuit is inhibited and which issturdy can be provided.

According to an embodiment of the disclosed invention, simplification ofa structure and a reduction in cost of an e-book reader are possible.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are views illustrating one mode of an e-book reader;

FIGS. 2A to 2C are views illustrating one mode of an e-book reader;

FIGS. 3A to 3C are views illustrating one mode of an e-book reader;

FIGS. 4A to 4C are views illustrating one mode of an e-book reader;

FIG. 5 is a view illustrating one mode of a circuit included in abinding portion of an e-book reader;

FIGS. 6A to 6D are views each illustrating one mode of an e-book reader;

FIGS. 7A and 7B are views illustrating one mode of an e-book reader;

FIGS. 8A to 8C are views each illustrating one mode of an e-book reader;

FIGS. 9A to 9C are views each illustrating one mode of an e-book reader;

FIGS. 10A to 10C are views each illustrating one mode of an e-bookreader;

FIGS. 11A and 11B are views illustrating one mode of an e-book reader;

FIG. 12 is a view illustrating one mode of an e-book reader;

FIGS. 13A and 13B are views illustrating one mode of an e-book reader;

FIGS. 14A and 14B are views illustrating one mode of an e-book reader;

FIGS. 15A and 15B are views illustrating one mode of an e-book reader;

FIG. 16 is a block diagram illustrating one mode of an e-book reader;

FIGS. 17A to 17C are views each illustrating one mode of a displaypanel;

FIGS. 18A and 18B are views each illustrating one mode of a displaypanel;

FIG. 19 is a view illustrating one mode of a display panel;

FIG. 20 is a view illustrating one mode of a display panel;

FIGS. 21A to 21D are views each illustrating one mode of a transistorthat is applicable to an e-book reader; and

FIG. 22 is a view illustrating one mode of a display panel.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, Embodiments are described in detail using the drawings.Note that the present invention is not limited to the description of theembodiments, and it is apparent to those skilled in the art that themodes and details can be modified in various ways without departing fromthe spirit of the present invention disclosed in this specification andthe like. Structures of different embodiments can be implemented in anappropriate combination. On the description of the invention withreference to the drawings, a reference numeral indicating the same partis used in common throughout different drawings, and description on thesame part is omitted.

Note that the size, the thickness of a layer, or a region of eachstructure illustrated in drawings or the like in embodiments isexaggerated for simplicity in some cases. Embodiments of the presentinvention therefore are not limited to such scales.

Note that the terms “first”, “second”, “third” and the like in thisspecification are used in order to avoid confusion between componentsand do not set a limitation on number.

Embodiment 1

In Embodiment 1, an example of an e-book reader will be described withreference to drawings.

An e-book reader described in this embodiment includes a plurality ofdisplay panels each including a display portion in which display controlis performed by a scan line driver circuit and a signal line drivercircuit, and a binding portion fastening the plurality of display panelstogether. The signal line driver circuit is provided inside the bindingportion, and the scan line driver circuit is provided for each of theplurality of display panels.

FIGS. 1A to 1C illustrate, as an example of the e-book reader includingthe plurality of display panels, an e-book reader in which a bindingportion 4308 is provided at edges of two display panels (a first displaypanel 4311 and a second display panel 4312). Hereinafter, the e-bookreader including the first display panel and the second display panel isspecifically described with reference to FIGS. 1A to 1C. Note that FIG.1A illustrates the opened e-book reader, FIG. 1B illustrates the closede-book reader, and FIG. 1C illustrates the half-opened e-book reader.

The e-book reader illustrated in FIGS. 1A to 1C includes the firstdisplay panel 4311 including a first display portion 4301, the seconddisplay panel 4312 including a second display portion 4307, the bindingportion 4308 provided at one edge of each of the first display panel4311 and the second display panel 4312, scan line driver circuits 4321 aand 4321 b controlling display of the first display portion 4301, scanline driver circuits 4322 a and 4322 b controlling display of the seconddisplay portion 4307, and a signal line driver circuit 4323 controllingdisplay of the first display portion 4301 and the second display portion4307.

The scan line driver circuits 4321 a and 4321 b are provided for thefirst display panel 4311, the scan line driver circuits 4322 a and 4322b are provided for the second display panel 4312, and the signal linedriver circuit 4323 is provided inside the binding portion 4308.

The first display panel 4311 can be flexible. In that case, a pixelcircuit included in the first display portion 4301 and the scan linedriver circuits 4321 a and 4321 b may be provided over a flexiblesubstrate such as a plastic substrate.

The second display panel 4312 can also be flexible, like the firstdisplay panel 4311. In that case also, a pixel circuit included in thesecond display portion 4307 and the scan line driver circuits 4322 a and4322 b may be provided over a flexible substrate such as a plasticsubstrate.

The binding portion 4308 is preferably less flexible (more rigid) thanat least the first display panel 4311 and the second display panel 4312.For example, a housing forming the binding portion 4308 can be formedusing plastic, metal, or the like which is thicker than the firstdisplay panel 4311 and the second display panel 4312. In that case, thee-book reader can be bent (warped) at a portion other than the bindingportion 4308.

There is no particular limitation on the location where the bindingportion 4308 is provided. For example, the binding portion 4308 can beprovided along one edge of each of the first display panel 4311 and thesecond display panel 4312. For example, as illustrated in FIGS. 1A to1C, in the case where the first display panel 4311 and the seconddisplay panel 4312 have rectangular shapes, the binding portion 4308 canbe provided along predetermined sides of the first display panel 4311and the second display panel 4312 (so that the sides are fastenedtogether). Note that the “rectangular shape” here includes a shape inwhich a corner of the rectangular is rounded.

The signal line driver circuit 4323 is provided inside the bindingportion 4308. For example, the binding portion 4308 is formed using acolumnar housing with a hollow or a cylindrical housing with a hollow,and the signal line driver circuit 4323 can be provided in the hollow.When the signal line driver circuit 4323 is provided inside the bindingportion 4308, damage to the signal line driver circuit 4323 due to thebend of the display panel can be prevented.

Further, as illustrated in FIGS. 1A to 1C, the scan line driver circuits4321 a and 4321 b are preferably provided at edges of the first displaypanel 4311 in a direction perpendicular or substantially perpendicularto the binding portion 4308. Similarly, the scan line driver circuits4322 a and 4322 b are preferably provided at edges of the second displaypanel 4312 in a direction perpendicular or substantially perpendicularto the binding portion 4308. As a result, leading of a wiring can bereduced and the structure can be simplified in comparison with the casewhere the scan line driver circuit and the signal line driver circuitare provided in one portion (e.g., inside the binding portion 4308).

Further, when the scan line driver circuits 4321 a and 4321 b and apixel circuit included in the first display portion 4301 are formed overa flexible substrate through the same process, the scan line drivercircuits 4321 a and 4321 b can be bent and a reduction in cost can beachieved. Similarly, when the scan line driver circuits 4322 a and 4322b and a pixel circuit included in the second display portion 4307 areformed over a flexible substrate through the same process, the scan linedriver circuits 4322 a and 4322 b can be bent and a reduction in costcan be achieved.

The pixel circuit included in the first display portion 4301, the pixelcircuit included in the second display portion 4307, and elementsincluded in the scan line driver circuits 4321 a, 4321 b, 4322 a, and4322 b can be formed using thin film transistors or the like. On theother hand, a circuit which is driven at a high speed such as the signalline driver circuit 4323 can be formed using an integrated circuit (IC)formed using an SOI substrate or a semiconductor substrate such as asilicon substrate, and the IC can be provided inside the binding portion4308.

When an IC in which the circuit which is driven at a high speed such asthe scan line driver circuit is provided inside the binding portion, andthe scan line driver circuit and the pixel circuit included in thedisplay portion are formed with elements such as thin film transistorsover a flexible substrate as described above, the display panel can bebent easily, destruction of the IC due to the bending of the displaypanel can be inhibited, and a reduction in cost can be achieved incomparison with the case where the signal line driver circuit and thescan line driver circuit are provided with an IC. In addition, when thescan line driver circuit is provided on the display panel at the edge ofthe display panel in a direction perpendicular to the binding portion,leading of a wiring can be suppressed and the structure can besimplified.

Note that, although the case where the scan line driver circuits areprovided at both edges of the first display panel 4311 is illustrated inFIGS. 1A to 1C, the scan line driver circuit (either one of the scanline driver circuit 4321 a and the scan line driver circuit 4321 b) maybe provided at one of the edges. Similarly, although the case where thescan line driver circuits are provided at both edges of the seconddisplay panel 4312 is illustrated, the scan line driver circuit may beprovided at one of the edges.

Embodiment 1 can be implemented by being combined with any of thestructures described in the other embodiments as appropriate.

Embodiment 2

In Embodiment 2, a specific structure of the above e-book readerillustrated in FIGS. 1A to 1C will be described with reference todrawings. Note that since the structure described in this embodiment isin common with that described in Embodiment 1 in many points,description of the common points will be omitted and different pointswill be described in detail in the following description.

The specific structure of the e-book reader is described with referenceto FIGS. 2A to 2C. FIG. 2A is a plan view of the closed e-book reader,FIG. 2B is a cross-sectional view taken along the line A-B of FIG. 2A,and FIG. 2C is a detailed schematic view of the cross section.

As for the e-book reader illustrated in FIGS. 2A to 2C, the bindingportion 4308 is formed using a housing with a hollow, and the signalline driver circuit 4323 is provided inside the housing. Here, thesignal line driver circuit 4323 is formed with an IC, and the IC isprovided inside the binding portion 4308. The IC can be formed using anSOI substrate, a semiconductor substrate such as a silicon substrate, orthe like. Needless to say, a circuit (e.g., a CPU or a memory) otherthan the signal line driver circuit can be provided for the IC.

Further, FIGS. 2A to 2C illustrate the case where the IC provided insidethe binding portion 4308 is mounted on a flexible printed circuit (FPC)by a tape automated bonding (TAB) method.

More specifically, a signal line driver circuit 4323 a controlling thefirst display portion 4301 is provided on an FPC 4324 a, a signal linedriver circuit 4323 b controlling the second display portion 4307 isprovided on an FPC 4324 b, and the signal line driver circuit 4323 a andthe signal line driver circuit 4323 b are electrically connected to eachother through a printed board 4325. The FPC 4324 a is electricallyconnected to the first display panel 4311 and the printed board 4325.The FPC 4324 b is electrically connected to the second display panel4312 and the printed board 4325.

In FIGS. 2A to 2C, the printed board 4325 can be provided to be incontact with the housing forming the binding portion 4308. In that case,the first display panel 4311 and the second display panel 4312 arefastened together by the binding portion 4308.

As illustrated in FIGS. 2A to 2C, in the case where the signal linedriver circuit is provided on the FPC, a stress concentration region4326 is preferably provided in one or both of the first display panel4311 and the second display panel 4312. The provision of the stressconcentration region 4326 in the display panel makes it possible toreduce the stress which is applied to the FPC when the e-book reader isopened (when the first display panel 4311 and/or the second displaypanel 4312 are/is bent) and to inhibit the destruction of the signalline driver circuit provided on the FPC.

Note that the “stress concentration region” refers to a region wherestress is concentrated, which is formed by deformation of a material dueto cutting or the like, bending due to attachment of a material or thelike, or a change in strength against extension. Specifically, thestress concentration region 4326 can be formed by provision of a cutportion (a depressed portion or a groove) in a part of the first displaypanel 4311 or the second display panel 4312 at which the first displaypanel 4311 or the second display panel 4312 is to be bent.

For example, the first display panel 4311 can be formed using an elementsubstrate 4331 a and a sealing substrate 4332 a, and one or both of theelement substrate 4331 a and the sealing substrate 4332 a can beprovided with a cut portion. FIGS. 2A to 2C illustrate the case wherethe cut portion is provided in the sealing substrate 4332 a to form thestress concentration region 4326. In addition, in the structuredescribed here, the scan line driver circuits 4321 a and 4321 b and apixel circuit which drives the first display portion 4301 can be formedon the element substrate 4331 a so as to be electrically connected tothe FPC 4324 a.

Similarly, the second display panel 4312 can be formed using an elementsubstrate 4331 b and a sealing substrate 4332 b, and one or both of theelement substrate 4331 b and the sealing substrate 4332 b can beprovided with a cut portion. Note that the scan line driver circuits4322 a and 4322 b and a pixel circuit which drives the second displayportion 4307 can be formed on the element substrate 4331 b so as to beelectrically connected to the FPC 4324 b.

Further, the stress concentration region 4326 may be provided along adirection in which the first display panel 4311 and the second displaypanel 4312 are to be bent. For example, in FIG. 2A, when the cut portionis provided from an upper end to a bottom end of the first display panel4311 and/or the second display panel 4312 along a direction which isparallel or substantially parallel to the binding portion 4308, thedirection in which the display panel is bent can be controlled (thedisplay panel can be selectively bent in a direction perpendicular tothe binding portion) and the destruction of the signal line drivercircuit provided on the FPC can be inhibited.

The stress concentration region 4326 can be provided inside or outsidethe binding portion 4308. For example, the stress concentration region4326 is preferably provided outside the binding portion 4308 (e.g.,between the binding portion 4308 and the display portion) in the casewhere the binding portion 4308 is provided so as to be close to thefirst display panel 4311 or the second display panel 4312 with the firstdisplay panel 4311 and the second display panel closed.

In FIGS. 2A to 2C, the signal line driver circuit 4323 a controlling thefirst display portion 4301 and the signal line driver circuit 4323 bcontrolling the second display portion 4307 are formed using differentICs, and the signal line driver circuit 4323 a and the signal linedriver circuit 4323 b are electrically connected to each other throughthe printed board 4325. However, the present invention is not limitedthereto. The signal line driver circuit 4323 a and the signal linedriver circuit 4323 b may be built in one IC.

Next, a structure of the e-book reader which is different from thatillustrated in FIGS. 2A to 2C is described with reference to FIGS. 3A to3C. FIG. 3A is a plan view of the closed e-book reader, FIG. 3B is across-sectional view taken along the line A-B of FIG. 3A, and FIG. 3C isa detailed schematic view of the cross section.

FIGS. 3A to 3C illustrate the case where an IC provided in the bindingportion 4308 are mounted on the first display panel 4311 and the seconddisplay panel 4312 by a chip on glass (COG) method.

More specifically, the signal line driver circuit 4323 a controlling thefirst display portion 4301 is provided on the element substrate 4331 aincluded in the first display panel 4311, the signal line driver circuit4323 b controlling the second display portion 4307 is provided on theelement substrate 4331 b included in the second display panel 4312, andthe signal line driver circuit 4323 a and the signal line driver circuit4323 b are electrically connected to each other through the FPCs 4324 aand 4324 b and the printed board 4325.

As illustrated in FIGS. 3A to 3C, in the case where the signal linedriver circuit is provided on the display panel, similarly to the caseof FIGS. 2A to 2C, the stress concentration region 4326 is preferablyprovided for one or both of the first display panel 4311 and the seconddisplay panel 4312. In that case, the stress concentration region 4326is provided in a region which is different from (is provided so as toavoid) the region in which the signal line driver circuit is provided.For example, when the stress concentration region 4326 is provided onthe sealing substrate side, the stress which is applied to the signalline driver circuit when the e-book reader is opened (when the firstdisplay panel 4311 and/or the second display panel 4312 are/is bent) canbe reduced and the destruction of the signal line driver circuit can beinhibited.

Next, a structure of the e-book reader which is different from thoseillustrated in FIGS. 2A to 2C and FIGS. 3A to 3C is described withreference to FIGS. 4A to 4C. FIG. 4A is a plan view of the closed e-bookreader, FIG. 4B is a cross-sectional view taken along the line A-B ofFIG. 4A, and FIG. 4C is a detailed schematic view of the cross section.

FIGS. 4A to 4C illustrate an e-book reader of the case where an IC inwhich a circuit such as a signal line driver circuit is formed isprovided on a printed board, and the printed board and a display panelare connected with an FPC.

More specifically, the signal line driver circuit 4323 a controlling thefirst display portion 4301 is provided on a printed board 4327 a, thesignal line driver circuit 4323 b controlling the second display portion4307 is provided on a printed board 4327 b, and the signal line drivercircuit 4323 a and the signal line driver circuit 4323 b areelectrically connected to each other through an FPC 4329. The FPC 4329is electrically connected to the printed board 4327 a and the printedboard 4327 b, the FPC 4324 a is electrically connected to the firstdisplay panel 4311 and the printed board 4327 a, and the FPC 4324 b iselectrically connected to the second display panel 4312 and the printedboard 4327 b.

In FIGS. 4A to 4C, since the display panels can be bent with the FPC4324 a and the FPC 4324 b, a stress concentration region is not providedfor the first display panel 4311 and the second display panel 4312.

Next, examples of the binding portion 4308 and a configuration of acircuit which can be provided in the binding portion 4308 are describedwith reference to FIG. 5.

FIG. 5 illustrates the case where a display control portion 200including the signal line driver circuits is incorporated in the bindingportion 4308. As described above, the circuit can be formed using an ICformed using an SOI substrate, a semiconductor substrate such as asilicon substrate, or the like.

The display control portion 200 can include a CPU 201, a memory portion203, a power feeding portion 205, a power supply circuit 207, an imagesignal generation circuit 215, the signal line driver circuits 4323 aand 4323 b, an operation portion 219, and the like, which can beconnected to each other through an interface or the like. The displaycontrol portion 200 is electrically connected to the first display panel4311 and the second display panel 4312. Although the operation portion219 is provided in the binding portion 4308 here, the operation portion219 can be provided on the first display panel 4311 and/or the seconddisplay panel 4312.

The CPU 201 controls the operation of the whole e-book reader.

Information to be displayed on the first display portion 4301 and/or thesecond display portion 4307 is inputted to a data input portion 211 froman external device. Note that the data input portion 211 may be providedwith an antenna 216 for transmitting/receiving data to/from an externaldevice. In that case, the data input portion 211 has a function oftransferring data received by the antenna 216 or data stored in a memorymedium (an external memory 213) to an internal memory 209.

The memory portion 203 can include the internal memory 209, the datainput portion 211, and the external memory 213. Information to bedisplayed on the first display portion 4301 and/or the second displayportion 4307, a program for operating the e-book reader, or the like canbe recorded in the internal memory 209, the data input portion 211, andthe external memory 213.

The internal memory 209 includes a memory portion for storing a programfor processing with the CPU 201 a signal outputted to the image signalgeneration circuit 215 and/or the power supply circuit 207 on the basisof a signal from the power feeding portion 205, the operation portion219, or the like, data transferred from the data input portion 211, orthe like. As examples of the internal memory 209, a dynamic randomaccess memory (DRAM), a static random access memory (SRAM), a mask readonly memory (ROM), a programmable read only memory (PROM), and the likeare given.

As an example of the external memory 213, a memory medium such as an ICcard or a memory card is given.

The power feeding portion 205 includes a secondary battery, a capacitor,and the like. A reduction in size of the power feeding portion 205 ispossible when, for example, a lithium battery, preferably, a lithiumpolymer battery utilizing a gel electrolyte, a lithium ion battery, orthe like is used as the secondary battery. Needless to say, any batterycan be used as long as it can be charged, and a battery that can becharged and discharged, such as a nickel-metal hydride battery, anickel-cadmium battery, an organic radical battery, a lead storagebattery, an air secondary battery, a nickel-zinc battery, or asilver-zinc battery may be used. As the capacitor, an electric doublelayer capacitor, a lithium ion capacitor, another capacitor with highcapacitance, or the like can be used. The capacitor is preferably usedbecause it is less likely to be deteriorated even when the number ofcharging and discharging is increased and is excellent in rapidcharging. The power feeding portion 205 may be sheet-like,cylinder-like, prism-like, plate-like, coin-like, or the like asappropriate.

Further, the power feeding portion 205 can have a structure to whichelectric power is wirelessly supplied. In that case, an antenna may beprovided for the power feeding portion 205.

The power supply circuit 207 is a circuit for controlling power supplyto a display element in accordance with the control by the CPU 201, inorder to perform display and non-display on the first display panel 4311and the second display panel 4312.

The operation portion 219 can be provided with a keyboard, an operationbutton, or the like. In the case where the operation portion 219 isprovided in the first display panel 4311 and/or the second display panel4312, the first display portion 4301 and/or the second display portion4307 can function as a touch display, and thus the display portion canalso function as an operation portion.

The structure in which the display control portion 200 is incorporatedin the binding portion 4308 is illustrated in FIG. 5, and a so-calledpower device such as a switching power source or a DC-DC converter mayfurther be provided.

Further, in the e-book reader illustrated in FIG. 5, by operation of theoperation portion 219, power input and switching of display can beperformed. Further, the e-book reader can be operated in such a mannerthat the first display portion 4301 and/or the second display portion4307 are/is touched with a finger or an input pen to be treated as atouch display.

As described above, when the display control portion 200 is incorporatedin the binding portion 4308, the display control portion 200 can beprotected by a housing. In addition, a reduction in thickness of thee-book reader is possible.

In Embodiments 1 and 2, the scan line driver circuits 4321 a and 4321 bare provided on the first display panel 4311 along the first displayportion 4301 in a direction perpendicular to the binding portion 4308,and the scan line driver circuits 4322 a and 4322 b are provided on thesecond display panel 4312 along the second display portion 4307 in adirection perpendicular to the binding portion 4308. However, thepresent invention is not limited thereto.

For example, as illustrated in FIG. 6A, in the first display panel 4311,the scan line driver circuits 4321 a and 4321 b can be provided so thatthe distance between the scan line driver circuits 4321 a and 4321 b andthe binding portion 4308 is larger than that between the first displayportion 4301 and the binding portion 4308. In general, since the scanline driver circuits 4321 a and 4321 b each have a higher concentrationof elements than the pixel circuit, the scan line driver circuits 4321 aand 4321 b are not provided in the part at which the first display panel4311 is bent. Accordingly, the destruction of the scan line drivercircuits 4321 a and 4321 b can be inhibited.

As illustrated in FIGS. 6B and 6C, each of the scan line driver circuits4321 a and 4321 b can be divided into a plurality of circuit portions,and the plurality of circuit portions can be spaced from each other.Consequently, even in the case where the first display panel 4311 isbent, stress applied to the scan line driver circuits 4321 a and 4321 bcan be reduced and the destruction of the scan line driver circuits 4321a and 4321 b can be inhibited. In FIG. 6B, each of the scan line drivercircuits 4321 a and 4321 b is divided into two circuit portions. In FIG.6C, each of the scan line driver circuits 4321 a and 4321 b is dividedinto four circuit portions. However, the number of divided scan linedriver circuits is not limited thereto.

As illustrated in FIG. 6D, in the first display panel 4311, the scanline driver circuit (either one of the scan line driver circuit 4321 aand the scan line driver circuit 4321 b) may be provided at one of theedges. This makes it possible to reduce the frame size of the e-bookreader.

Note that the structures illustrated in FIGS. 6A to 6D can also beapplied to the second display panel 4312.

Embodiment 2 can be implemented by being combined with any of thestructures described in the other embodiments as appropriate.

Embodiment 3

In Embodiment 3, an example of a function of the above embodiments inthe case where an e-book reader including a plurality of flexibledisplay panels is opened and bent to be used will be described withreference to FIGS. 7A and 7B, FIGS. 8A to 8C, FIGS. 9A to 9C, and FIGS.10A to 10C.

First, a front plan view of FIG. 7A illustrating the case where a useropens an e-book reader to use and a top plan view of FIG. 7B of the caseof FIG. 7A are described.

The e-book reader illustrated in FIG. 7A includes the first displaypanel 4311, the second display panel 4312, and the binding portion 4308.The first display panel 4311 includes the first display portion 4301,and display on the first display portion 4301 is controlled by the scanline driver circuit 4321 for supplying a scan signal to the firstdisplay portion 4301 and the signal line driver circuit 4323 a forsupplying an image signal to the first display portion 4301. The seconddisplay panel 4312 includes the second display portion 4307, and displayon the second display portion 4307 is controlled by the scan line drivercircuit 4322 for supplying a scan signal to the second display portion4307 and the signal line driver circuit 4323 b for supplying an imagesignal to the second display portion 4307. Further, user's hands 4350 aand 4350 b gripping the edges of the first display panel 4311 and thesecond display panel 4312 are also illustrated in FIG. 7A. Further, inthe front plan view of FIG. 7A, a line of sight at the time when theuser is looking at the e-book reader illustrated in the top plan view ofFIG. 7B from above is also illustrated.

In the top plan view of FIG. 7B, the first display panel 4311, thesecond display panel 4312, and the binding portion 4308 are illustrated.As illustrated in FIG. 7B, when the user opens the e-book with his/herhands 4350 a and 4350 b to use, bending portions (hereinafter, referredto as “bending portions C”) are formed in areas indicated by arrows Cand non-bending portions (hereinafter, referred to as “non-bendingportions D”) are formed in areas indicated by arrows D in the flexibledisplay panels.

Note that in FIG. 7B, as an example, description is made on the casewhere the bending portions C of the first display panel 4311 and thesecond display panel 4312 are positioned on the side near the bindingportion 4308 and the non-bending portions D of the first display panel4311 and the second display panel 4312 are positioned on the side awayfrom the binding portion 4308. The bending state of the display panel isdifferent between the bending portion C and the non-bending portion Ddepending on the structure of the binding portion 4308 and a material ofa substrate included in the display panel. For the above reason, thebending portions C of the first display panel 4311 and the seconddisplay panel 4312 may be positioned on the side away from the bindingportion 4308 and the binding portions B of the first display panel 4311and the second display panel 4312 may be positioned on the side near thebinding portion 4308.

Note that since the e-book reader has a structure in which the displaypanels are fastened together by the binding portion 4308, the bendingportion C and the non-bending portion D are formed at edge portions ofeach of the first display panel 4311 and the second display panel 4312which are in a direction (indicated by an arrow 7002 in FIG. 7B)perpendicular to a direction in which the binding portion 4308 extends.Thus, by the binding portion 4308, the signal line driver circuit 4323 aand the signal line driver circuit 4323 b can be prevented fromdestruction caused by the bending of the display panels. Further, eachof the scan line driver circuit 4321 and the scan line driver circuit4322 which are provided in the non-bending portions D in FIGS. 7A and 7Bcan be manufactured in the process of forming the display portion,leading to a reduction in cost and a reduction of leading of a wiring tothe display portion. Note that a plurality of bending portions C and/ora plurality of non-bending portions D may be provided, and the bendingportion C and the non-bending portion D may be provided alternately. Astress concentration region may be provided for the display panel toartificially form the bending portion C and the non-bending portion D.

FIGS. 8A to 8C, like FIG. 7A, are front plan views illustrating the casewhere a user opens the e-book reader to use. The arrangement of the scanline driver circuit 4321 and the scan line driver circuit 4322 each withrespect to the bending portion C and the non-bending portion D isdescribed with reference to FIGS. 8A to 8C.

In FIG. 8A, the bending portion C is positioned on the side near thebinding portion 4308 while the bending portion D is positioned on theside away from the binding portion 4308. Accordingly, each of the scanline driver circuit 4321 and the scan line driver circuit 4322 ispositioned in the non-bending portion D which is on the side away fromthe binding portion 4308. Note that a scan signal may be supplied to apixel TFT 4352 in the display portion by leading of a wiring extendingfrom each of the scan line driver circuit 4321 and the scan line drivercircuit 4322, to each scan line of the display portion. Note that acontrol signal such as a clock signal for driving each of the scan linedriver circuit 4321 and the scan line driver circuit 4322 is suppliedthrough a wiring extending from an image signal generation circuit inthe binding portion 4308. A wiring for electrically connecting circuitsis formed by microfabrication of a metal film or the like, and asemiconductor film of a transistor included in the scan line drivercircuit is formed using a semiconductor material such as a silicon film.A metal film has higher ductibility and less damage caused by bendingthan a semiconductor material. For the above reason, a wiring which isconnected to the scan line driver circuit is provided in a portioncorresponding to the bending portion C and the transistor included inthe scan line driver circuit is provided in a portion corresponding tothe non-bending portion D, whereby damage to the semiconductor film ofthe transistor caused by bending can be reduced. As a result, thearrangement of the scan line driver circuit 4321 and the scan linedriver circuit 4322 as in FIG. 8A makes it possible to inhibitdestruction of the circuit at the time when a user opens the e-bookreader with his/her hands 4350 a and 4350 b to use.

FIG. 8B illustrates a structure in which the bending portions C and thenon-bending portions D are provided alternately from the side near thebinding portion 4308 and the side away therefrom. Accordingly, the scanline driver circuit 4321 and the scan line driver circuit 4322 each aredivided into plural circuits and the plural circuits are spaced fromeach other in the non-binding portions B. Note that a scan signal may besupplied to the pixel TFT 4352 in the display portion by leading of awiring extending from each of the scan line driver circuit 4321 and thescan line driver circuit 4322, to each scan line of the display portion.Note that a control signal such as a clock signal for driving each ofthe scan line driver circuit 4321 and the scan line driver circuit 4322is supplied through a wiring extending from an image signal generationcircuit in the binding portion 4308. A signal which is transmittedbetween pulse signal generating circuits such as flip flops included inthe scan line driver circuit may be supplied through a wiring. A wiringfor electrically connecting circuits is formed by microfabrication of ametal film or the like, and a semiconductor film of a transistorincluded in the scan line driver circuit is formed using a semiconductormaterial such as a silicon film. A metal film has higher ductibility andless damage caused by bending than a semiconductor material. For theabove reason, a wiring which is connected to the scan line drivercircuit is provided in a portion corresponding to the bending portion Cand the transistor included in the scan line driver circuit is providedin a portion corresponding to the non-bending portion D, whereby damageto the semiconductor film of the transistor caused by bending can bereduced. Further, in FIG. 8B, the scan line driver circuit is dividedinto plural circuits and the plural circuits are spaced from each other,whereby stress applied to the scan line driver circuits at the time ofbending can be dispersed. As a result, the arrangement of the scan linedriver circuit 4321 and the scan line driver circuit 4322 as in FIG. 8Bmakes it possible to more effectively inhibit destruction of the circuitat the time when a user opens the e-book reader with his/her hands 4350a and 4350 b to use.

Note that in FIG. 8B, the scan line driver circuits 4321 may be providedon opposite sides in the display portion as the scan line drivercircuits 4321 a and the scan line driver circuit 4321 b, and the scanline driver circuits 4322 may be provided on opposite sides in thedisplay portion as the scan line driver circuits 4322 a and the scanline driver circuit 4322 b so as to obtain a redundant structure orspread the function of outputting a scan signal. FIG. 8C is a viewillustrating a structure in which the scan line driver circuitsdescribed in FIG. 8B are provided on the opposite sides in the displaypanel. Scan signals are supplied to the pixel TFT 4352 by the scan linedriver circuits 4321 a and the scan line driver circuits 4321 b providedon opposite sides and the scan line driver circuits 4322 a and the scanline driver circuits 4322 b provided on the opposite sides, whereby thenumber of a pulse signal generation circuit such as a flip flop includedin the scan line driver circuit can be reduced; thus, destruction of thecircuits at the time when a user opens the e-book reader with his/herhands 4350 a and 4350 b to use can be inhibited.

Advantages of arranging the scan line driver circuits not in the regionscorresponding to the bending portions C but in the regions correspondingto the non-bending portions D are described using FIGS. 8B and 8Cillustrating the specific examples. The structures make it possible todisperse stress applied to the scan line driver circuits at the time ofbending and to inhibit destruction of the circuits at the time when auser opens the e-book reader with his/her hands 4350 a and 4350 b touse.

Next, an example of providing a stress concentration region forartificially for forming the bending portion C and the non-bendingportion D in the display panel in the case where the plurality of drivercircuits are provided so as to be separated from each other as describedin FIGS. 8B and 8C is described with reference to FIGS. 9A to 9C andFIGS. 10A to 10C.

In FIG. 9A, the first display panel 4311, the binding portion 4308, thefirst display portion 4301, the scan line driver circuit 4321, and thesignal line driver circuit 4323 a are illustrated. The scan line drivercircuit 4321 is divided into two circuits and the two circuits arespaced from each other with a wiring 920 therebetween. It is preferablethat a stress concentration region 921 be formed so as to overlap thewiring 920. FIG. 9B is an example of a cross-sectional view taken in adirection perpendicular to the binding portion 4308. In FIG. 9B, a cutportion 922 a and a cut portion 922 b may be provided for a sealingsubstrate 923 and an element substrate 924 respectively in the stressconcentration region 921 which overlaps the wiring 920. Note that asillustrated in FIG. 9C, reinforcing plates 925 may be attached onto thescan line driver circuits 4321 of the element substrate 924 and thesealing substrate 923 to form the cut portion 922 a and the cut portion922 b. Note that the cut portion 922 a and the cut portion 922 b may beprovided so as to be parallel to the long axis of the binding portion4308 or may be provided partly.

Note that the stress concentration means a region where stress formed bydeformation of a material due to cutting or the like or a change in thestrength against bending or extension due to attachment of a material orthe like is concentrated.

Note that division of the scan line driver circuit means that the scanline driver circuit is divided into plural circuits in such a mannerthat repeated regions in the scan line driver circuit, in each of whicha wiring and a circuit element such as a TFT coexist are divided byregions used for wiring leading.

Further, in FIG. 10A, as in FIG. 9A, the first display panel 4311, thebinding portion 4308, the first display portion 4301, the scan linedriver circuit 4321, and the signal line driver circuit 4323 a areillustrated. The scan line driver circuit 4321 is divided into fourcircuits and the four circuits are spaced from each other with aplurality of wirings 920 therebetween. It is preferable that the stressconcentration regions 921 be formed to overlap the plurality of wirings920. FIG. 10B is an example of a cross-sectional view taken in adirection perpendicular to the binding portion 4308. In FIG. 10B, aplurality of cut portions 922 a and a plurality of cut portions 922 bmay be provided for the sealing substrate 923 and the element substrate924 respectively in the stress concentration regions 921 which overlapthe wirings 920. Note that as illustrated in FIG. 10C, the reinforcingplates 925 may be attached onto the scan line driver circuits 4321 ofthe element substrate 924 and the sealing substrate 923 to form theplurality of cut portions 922 a and the plurality of cut portions 922 b.Note that the plurality of cut portions 922 a and the plurality of cutportions 922 b may be provided so as to be parallel to the long axis ofthe binding portion 4308 or may be provided partly.

Note that the number of divisions of the scan line driver circuitillustrated in FIGS. 9A to 9C and FIGS. 10A to 10C are examples fordescription; the scan line driver circuit is divided as appropriate intoany number of circuits to be provided.

As described above, the structure of this embodiment makes it possibleto more effectively inhibit destruction of the scan line driver circuitat the time when a user opens the e-book reader to use. In addition,according to the structure of this embodiment, the stress concentrationregion is provided for the display panel in advance by the cut portionor the like, destruction of the scan line driver circuit can beinhibited more effectively.

Embodiment 3 can be implemented by being combined with any of thestructures described in the other embodiments as appropriate.

Embodiment 4

In Embodiment 4, an example of an e-book reader which has a structure inwhich a third panel of dual display type is provided between the firstdisplay panel 4311 and the second display panel 4312 in addition to thestructure described in Embodiment 1 in which the plurality of displaypanels are included will be described. FIG. 11A illustrates an openede-book reader and FIG. 11B illustrates a closed e-book reader. Inaddition, FIG. 12 is a cross-sectional view in a lateral direction.

The e-book reader illustrated in FIGS. 11A and 11B includes the firstdisplay panel 4311 including the first display portion 4301, the seconddisplay panel 4312 including an operation portion 4304 and the seconddisplay portion 4307, a third display panel 4313 including a thirddisplay portion 4302 and a fourth display portion 4310, and the bindingportion 4308 provided at edges of the first display panel 4311, thesecond display panel 4312, and the third display panel 4313. The thirddisplay panel 4313 is interposed between the first display panel 4311and the second display panel 4312. The e-book reader illustrated inFIGS. 11A and 11B includes four display screens: the first displayportion 4301, the second display portion 4307, the third display portion4302, and the fourth display portion 4310.

The first display panel 4311, the second display panel 4312, and thethird display panel 4313 are flexible and thus are easily bent. Further,when a plastic substrate is used for each of the first display panel4311 and the second display panel 4312 and a thin film is used for thethird display panel 4313, a thin e-book reader can be obtained. In otherwords, an e-book reader in which the third display panel 4313 is bentmore easily than the first display panel 4311 and the second displaypanel 4312, like the e-book reader the cross section of which in alateral direction is illustrated as an example in FIG. 12 can beobtained. When hard display panels are provided outside the thirddisplay panel 4313, the e-book reader can be handled like a book and thedestruction of the third display panel 4313 can be inhibited.

The third display panel 4313 is a dual display panel including the thirddisplay portion 4302 and the fourth display portion 4310. For the thirddisplay panel 4313, a display panel of a dual emission type may be used,or display panels of a one-side emission type may be attached.Alternatively, two liquid crystal display panels with a backlight(preferably, a thin EL panel) interposed therebetween may be used.

Further, the e-book reader illustrated in FIGS. 11A and 11B includesscan line driver circuits (not illustrated) controlling the firstdisplay portion 4301; scan line driver circuits 4322 a and 4322 bcontrolling the second display portion 4307; scan line driver circuits(not illustrated) controlling the third display portion 4302 and/or thefourth display portion 4310; and signal line driver circuit 4323controlling the first display portion 4301, the second display portion4307, the third display portion 4302, and/or the fourth display portion4310. Note that the scan line driver circuits 4321 a and 4321 b areprovided in the first display panel 4311, the scan line driver circuits4322 a and 4322 b are provided in the second display panel 4312, and thesignal line driver circuit 4323 is provided inside the binding portion4308.

Further, in the e-book reader illustrated in FIGS. 11A and 11B, thesecond display panel 4312 includes the operation portion 4304 whichfunctions as a switch for turning on, a switch for switching displays,or the like.

Further, the input operation of the e-book reader illustrated in FIGS.11A and 11B is performed when the first display portion 4301 or thesecond display portion 4307 is touched with a finger or an input pen orwhen the operation portion 4304 is operated. Note that a display button4309 displayed on the second display portion 4307 is illustrated in FIG.11A, and data input can be performed when the display button is touchedwith a finger or the like.

Further, as an usage example of the e-book reader in which the thirddisplay panel 4313 is interposed, which is illustrated in FIGS. 11A and11B, it is convenient to read text on the first display portion 4301 andthe fourth display portion 4310 and to see drawings on the seconddisplay portion 4307 and the third display portion 4302. Since imagescannot be displayed on the third display portion 4302 and the fourthdisplay portion 4310 at the same time, the display on the third displayportion 4302 is switched to the display on the fourth display portion4310 when a page is turned.

Further, after data on the first display portion 4301 and the thirddisplay portion 4302 are read in this order, the fourth display portion4310 and the second display portion 4307 display the next page when thethird display panel 4313 is turned at a certain angle. In addition,after data on the fourth display portion 4310 and the second displayportion 4307 are read, the third display portion 4302 and the firstdisplay portion 4301 display data on the next page when the thirddisplay panel 4313 is turned at a certain angle. This makes theswitching of display invisible, resulting in a reduction in visualdiscomfort or the like.

Next, an example of a specific structure of the e-book reader includingthe first display panel 4311, the second display panel 4312, and thethird display panel 4313 is described with reference to FIGS. 13A and13B, similarly to the description with reference to FIGS. 2A and 2B.Note that FIG. 13A is a plan view of the closed e-book reader and FIG.13B illustrates a cross section taken along the line A-B of FIG. 13A.

As for the e-book reader illustrated in FIGS. 13A and 13B, the bindingportion 4308 is formed using a housing with a hollow, and the signalline driver circuit is provided inside the housing. Here, the signalline driver circuit 4323 is formed using an IC, and the IC is providedinside the binding portion 4308. The IC can be formed using an SOIsubstrate, a semiconductor substrate such as a silicon substrate, or thelike. Needless to say, a circuit (e.g., a CPU or a memory) other thanthe signal line driver circuit can be provided for the IC.

Further, FIGS. 13A and 13B illustrate a case where the IC providedinside the binding portion is mounted on a flexible printed circuit(FPC) by a tape automated bonding (TAB) method.

More specifically, an IC in which the signal line driver circuit 4323controlling the first display portion 4301 is formed is provided on theFPC 4324; the IC in which the signal line driver circuit 4323controlling the second display portion 4307 is formed is similarlyprovided on the FPC 4324; an IC in which a signal line driver circuit4323 controlling the third display portion 4302 and the fourth displayportion 4310 is formed is provided on the FPC 4324; and the signal linedriver circuits 4323 are electrically connected to each other via theprinted board 4325. The FPCs 4324 are electrically connected to thefirst display panel 4311, the second display panel 4312, and the printedboard 4325.

In FIGS. 13A and 13B, the printed board 4325 can be provided so as to beattached to the housing forming the binding portion 4308.

In the case where the signal line driver circuit is provided on the FPCas illustrated in FIGS. 13A and 13B, the stress concentration region4326 is preferably provided for one or both of the first display panel4311 and the second display panel 4312 as described in FIG. 2C. Theprovision of the stress concentration region 4326 for the display panelmakes it possible to reduce the stress which is applied to the FPC 4324when the e-book reader is opened (when the first display panel 4311and/or the second display panel 4312 are/is bent) and to inhibit thedestruction of the signal line driver circuit 4323 provided on the FPC4324. Note that since the third display panel 4313 is formed using athin film, the e-book reader has enough flexibility to be used whilebeing opened; consequently, the e-book reader can be handled like abook.

Next, a structure of the e-book reader which is different from thatillustrated in FIGS. 13A and 13B is described with reference to FIGS.14A and 14B. FIG. 14A is a plan view of the closed e-book reader andFIG. 14B illustrates a cross section taken along the line A-B of FIG.14A.

FIGS. 14A and 14B illustrate an e-book reader of the case where an ICwhich is to be provided in the binding portion 4308 is mounted on thefirst display panel 4311 and the second display panel 4312 by a chip onglass (COG) method.

More specifically, an IC in which the signal line driver circuit 4323controlling the first display portion 4301 is formed is provided on anelement substrate which is included in the first display panel 4311; anIC in which the signal line driver circuit 4323 controlling the seconddisplay portion 4307 is formed is similarly provided on an elementsubstrate included in the second display panel 4313; an IC in which thesignal line driver circuit 4323 controlling the third display portion4302 and the fourth display portion 4310 is formed is provided on anelement substrate included in the third display panel 4313; and thesignal line driver circuits 4323 are electrically connected to eachother via the FPCs 4324 and the printed boards 4325.

Next, a structure of the e-book reader which is different from thatillustrated in FIGS. 13A and 13B and FIGS. 14A and 14B is described withreference to FIGS. 15A and 15B. FIG. 15A is a plan view of a closede-book reader and FIG. 15B illustrates a cross section taken along theline A-B of FIG. 15A.

FIGS. 15A and 15B illustrates an e-book reader of the case where an ICin which a circuit such as a signal line driver circuit is formed isprovided on a printed board, and the printed board and a display panelare connected with an FPC.

More specifically, an IC in which the signal line driver circuit 4323controlling the first display portion 4301 is formed is provided on theprinted board 4325; an IC in which the signal driver circuit 4323controlling the second display portion 4307 is formed is similarlyprovided on the printed board; an IC in which the signal line drivercircuit 4323 controlling the third display portion 4302 and the fourthdisplay portion 4310 is formed is provided on the element substrateincluded in the third display panel 4313; and the signal line drivercircuits 4323 are electrically connected to each other via the FPC 4324.The FPCs 4324 are electrically connected to the printed boards 4325.

In FIGS. 15A and 15B, since the display panel can be bent with the FPC4324, a bending portion is not necessarily provided.

Next, a structure of the e-book reader in which the third panel of adual display type is provided between the first display panel 4311 andthe second display panel 4312 and a function thereof are described usinga block diagram or the like. Note that the e-book reader in thisembodiment is particularly suitable for an e-book reader in which aself-luminous light-emitting element, a liquid crystal elementcontrolling transmission of light from a backlight or the like, or thelike is used as a light-emitting element in a display panel. Note thatanother display element such as an electrophoretic element can be usedas a display element of the e-book reader.

FIG. 16 is a block diagram of an e-book reader described in thisembodiment. The e-book reader illustrated in FIG. 16 includes a firstdisplay panel 701, a second display panel 702, a third display panel703, a fourth display panel 704, and a display control portion 705. Thefirst display panel 701 includes a scan line driver circuit 706A and afirst display portion 707A. The second display panel 702 includes a scanline driver circuit 706B and a second display portion 707B. The thirddisplay panel 703 includes a scan line driver circuit 706C and a thirddisplay portion 707C. The fourth display panel 704 includes a scan linedriver circuit 706D and a fourth display portion 707D.

Note that, as described in any of the above embodiments, the firstdisplay panel 701 to the fourth display panel 704 each are flexible andare fastened together by the binding portion in which the displaycontrol portion including the signal line driver circuit described inany of the above embodiments is provided.

Note that when a dual-emission type display panel is used as the thirddisplay panel 703 and the fourth display panel 704, the third panel 703can include both the third display portion 707 c and the fourth displayportion 707D, resulting in reduction in thickness and cost of the e-bookreader.

The first display portion 707A to the fourth display portion 707D eachinclude a plurality of pixels 708 each of which includes a pixel circuit710 for controlling a display element. Further, each of the pixelcircuits 710 includes a thin film transistor or the like. When the pixelcircuits 710 are formed at a time, a reduction in cost can be achieved.In addition, the first display portion 707A includes a photo sensor709A, the second display portion 707B includes a photo sensor 709B, thethird display portion 707C includes a photo sensor 709C, and the fourthdisplay portion 707D includes a photo sensor 709D.

Note that the scan line driver circuits 706A to 706D each supply a scansignal to the pixel circuit 710 in the pixel 708.

The photo sensors 709A to 709D each have a function of detecting a statein which data on the first display panel 701 and the third display panel703 are looked at or a state in which data on the second display panel702 and the fourth display panel 704 are looked at. The functiondescribed in this embodiment can be realized by a gradient detectionportion provided for the display panel or the like or anotheropening-closing detection unit.

Note that the photo sensor 709C and/or the photo sensor 709D can beomitted when the accuracy of illuminance of the photo sensor 709A and/orthe photo sensor 709B is increased. Note that a light-shielding portionis preferably provided instead of the photo sensor 709C and/or the photosensor 709D, in which case the accuracy of illuminance of the photosensor 709A and/or the photo sensor 709B and detection by the photosensor is possible even in the case where a light-transmitting substrateis used.

Note that the photo sensors 709A to 709D each may be formed as aphotosensor formed with a photodiode, a phototransistor, or the likeover a substrate over which the thin film transistor included in thepixel circuit 710 is formed. When the photo sensors 709A to 709D areformed together with the thin film transistors, a reduction in cost ofthe e-book reader can be achieved.

The display control portion 705 located in the binding portion includesa light intensity comparison circuit 711, a CPU 712, an internal memory713, an image signal generation circuit 714, a power supply circuit 715,signal transmission/reception portion 716, a power feeding portion 717,an operation portion 718, and a signal line driver circuits 714A to714D, which are connected to each other via an interface or the like.Note that the signal transmission/reception portion 716 may be providedwith an antenna portion 719 for transmitting/receiving data to/from anexternal device.

The light intensity comparison circuit 711 is a circuit which detectssignals from the photo sensors 709A to 709D and compares the intensityof the signals which corresponds to the illuminance. The light intensitycomparison circuit 711 encodes a signal corresponding to the obtainedintensity of each photo sensor. Then, the light intensity comparisoncircuit 711 compares signals corresponding to illuminance between thephoto sensor 709A and/or the photo sensor 709C included in the firstdisplay panel 701 and/or the third display panel 703 and the photosensor 709B and/or the photo sensor 709D included in the second displaypanel 702 and/or the fourth display panel 704. The signal after thecomparison is transmitted to the CPU 712, and the CPU 712 performsprocessing according to the signal. Note that the CPU 712 also performsprocessing according to the operation in the operation portion 718, orthe like.

The signal transmission/reception portion 716 has a function oftransferring, to the internal memory 713, data received by the antennaportion 719 or data stored in a recording medium. Data is stored in theinternal memory 713 via the interface or the like. Note that the datatransferred from the signal transmission/reception portion 716 to theinternal memory 713 may be information stored such as user ID, as wellas an image signal to be displayed on the display panel.

The internal memory 713 includes a memory portion which stores datatransferred from the signal transmittance/reception portion 716 and/or aprogram for processing, in the CPU 712, a signal to be outputted to theimage signal generation circuit 714 and/or the power supply circuit 715on the basis of a signal from the light intensity comparison circuit711, the power feeding portion 717, the operation portion 718, or thelike. For example, the internal memory 713 includes a read only memory(ROM) or a random access memory (RAM).

The power feeding portion 717 has a function of performing wired orwireless power feeding or power feeding by a power storage unit such asa battery or a capacitor. The operation portion 718 has a function ofencoding an operation by a user with a touch panel, an operation buttonwith which a movable portion can be operated and transferring theencoded operation to the CPU 712.

The image signal generation circuit 714 is a circuit for, depending onthe control of the CPU 712, supplying a clock signal, a start pulse, orthe like for driving the scan line driver circuit to each of the scanline driver circuits 706A to 706D in order to perform display andnon-display on the first display panel 701 to the fourth display panel704 and supplying a clock signal, a start pulse, an image signal, or thelike for driving the signal line driver circuit inside the bindingportion to each of the signal line driver circuits 714A to 714D.

Note that the signal line driver circuits 714A to 714D each supply animage signal to the pixel circuit 710 in the pixel 708 through a signalline.

The power supply circuit 715 is a circuit for controlling power supplyto a display element in accordance with control of the CPU 712 in orderto perform display and non-display on the first display panel 701 to thefourth display panel 704. In FIG. 16, for description, a power supplycircuit 715A which supplies electric power to the first display portion707A, a power supply circuit 715B which supplies electric power to thesecond display portion 707B, a power supply circuit 715C which supplieselectric power to the third display portion 707C, and a power supplycircuit 715D which supplies electric power to the fourth display portion707D are illustrated in the power supply circuit 715.

The performance of the e-book reader illustrated in FIG. 16 is describedusing one example. First, the light intensity comparison circuit 711compares the illuminance on display surfaces of the display panels,which is obtained by the photo sensors 709A to 709D. The CPU 712determines which display panel a user is looking at in accordance withthe result of the comparison by the light intensity comparison circuit711 or a signal from the operation portion 718. For example, the CPU 712determines that the user is looking at the first display portion 707Aand/or the third display portion 707C if the illuminance obtained by thephoto sensor 709A and/or the photo sensor 709C is higher than theilluminance obtained by the photo sensor 709B and/or the photo sensor709D according to the comparison. In accordance with the determinationof which display panel the user is looking at, the image signalgeneration circuit 714 controls an image signal and a control signalwhich are to be supplied to the first display panel 701 to the fourthdisplay panel 704 and/or the power supply circuit 715 controls powersupply to the first display panel 701 to the fourth display panel 704.Specifically, power supply to the second display panel 702 and thefourth display panel 704 which are provided with the second displayportion 707B and the fourth display portion 707D, respectively, at whichthe user is not looking is stopped, resulting in a reduction in powerconsumption and an increase in the life of the display panels.

As for the e-book reader illustrated in FIG. 16, a page at which a useris looking at is determined by the photo sensor and the light intensitycomparison circuit, whereby supply of an image signal, electric power,and the like to the display panel can be switched as appropriate.Consequently, the e-book reader in which a reduction in powerconsumption and an increase in the life of the display panel arerealized can be provided.

Embodiment 4 can be implemented by being combined with any of thestructures described in the other embodiments as appropriate.

Embodiment 5

In Embodiment 5, an example of a display panel provided in an e-bookreader will be described. A variety of display panels including anydisplay element can be employed, and the display panel may be either apassive-matrix type or an active-matrix type.

As the display panel, an electronic paper, a light-emitting displaypanel (electroluminescence panel), a liquid crystal display panel, orthe like can be used. The display panel is a panel in which a displayelement is sealed, and to which a connector such as a flexible printedcircuit (FPC), a tape automated bonding (TAB) tape, or a tape carrierpackage (TCP) is attached and an external circuit including a signalline driver circuit is electrically connected. An IC including a signalline driver circuit may be mounted onto the display panel by a chip onglass (COG) method.

As the display panel, either a dual display panel in which display isperformed on both sides or a single-side display panel in which displayis performed on one side may be used.

In Embodiment 4, the third display panel 4313 is a dual display panelincluding the third display portion 4302 and the fourth display portion4310. As the third display panel 4313, a dual-emission display panel maybe used or two one-side-emission display panels attached may be used.Two liquid crystal display panels with a backlight (preferably a thin ELpanel) therebetween may be used.

FIGS. 17A to 17C illustrate examples of the dual display panel using thethird display panel 4313. Note that in FIGS. 17A to 17C, each arrowindicates a direction in which light emission is extracted.

FIG. 17A illustrates the third display panel 4313 in which a displayelement 102 is provided between a substrate 100 and a substrate 101, andthe third display portion 4302 and the fourth display portion 4310 areprovided on the substrate 100 side and the substrate 101 side,respectively. Display is performed on the first display portion 4302 andthe fourth display portion 4310 by the display element 102; therefore,the substrates 100 and 101 have light-transmitting properties. It ispreferable that an EL element that is a self-luminous light-emittingelement be used as the display element 102. In the case of using lightentering the third display panel 4313, a liquid crystal display elementor an electrophoretic display element can be used as the display element102.

FIG. 17B illustrates a third display panel 4313 in which a single-sidedisplay panel in which a display element 114 is provided between asubstrate 110 and a substrate 112 and a single-side display panel inwhich a display element 115 is provided between a substrate 111 and asubstrate 113 are stacked, and the third display portion 4302 and thefourth display portion 4310 are provided on the substrate 100 side andthe substrate 101 side, respectively. Display is performed on the thirddisplay portion 4302 and the fourth display portion 4310 by the displayelement 114 and the display element 115, respectively; therefore, thesubstrates 110 and 111 have light-transmitting properties. To thecontrary, the substrate 112 and the substrate 113 do not necessarilyhave light-transmitting properties but may have light-reflectingproperties. The single-side display panels may be attached to each otherby bonding the substrates 112 and 113 with a bonding layer. Either oneof the substrate 112 and the substrate 113 may be provided.

It is preferable that EL elements be used as the display element 114 andthe display element 115. In the case of using light entering the thirddisplay panel 4313, a liquid crystal display element or anelectrophoretic display element can be used as each of the displayelement 114 and the display element 115. In order to enhance the lightextraction efficiency, a reflective display panel is preferably used asthe single-side display panel.

A backlight may be provided between light-transmissive liquid crystaldisplay panels to form the third display panel 4313. FIG. 17Cillustrates a third display panel 4313 in which a light-transmissiveliquid crystal display panel in which a display element 124 is providedbetween a substrate 120 and a substrate 122 and a light-transmissiveliquid crystal display panel in which a display element 125 is providedbetween a substrate 121 and a substrate 123 are stacked with a backlight126 which functions as a light source provided therebetween, and thethird display portion 4302 and the fourth display portion 4310 areprovided on the substrate 120 side and the substrate 121 side,respectively. Display is performed on the third display portion 4302 bylight from the backlight 126 and the display element 124 and display isperformed on the fourth display portion 4310 by light from the backlight126 and the display element 125; therefore, the substrates 120, 121,122, and 123 have light-transmitting properties.

The backlight may be attached with a bonding layer. Either one of thesubstrate 122 and the substrate 123 may be provided. It is preferablethat a thin EL panel be used as the backlight 126 because the thicknessof the display panel 4313 can be reduced.

In the case of a single-side display panel, a non-light-transmissive orreflective housing is preferably provided for the side on which adisplay portion is not provided, in which case the display panel can bereinforced.

Modes of the display panel are described below with reference to FIGS.18A and 18B, FIG. 19, and FIG. 20. FIGS. 18A and 18B, FIG. 19, and FIG.20 correspond to cross-sectional views along line M-N in FIG. 4A. FIGS.18A and 18B, FIG. 19, and FIG. 20 are examples of the case where the FPC4324 is attached to the first display panel 4311 including the firstdisplay portion 4301 including a pixel circuit and the scan line drivercircuit 4321 a; the display portion 4301 and the scan line drivercircuit 4321 a provided over the element substrate 4331 a are sealedwith the sealing substrate 4332 a by a sealant 4005.

As illustrated in FIGS. 18A and 18B, FIG. 19, and FIG. 20, the firstdisplay panel 4311 includes a connection terminal electrode 4015 and aterminal electrode 4016, and the connection terminal electrode 4015 andthe terminal electrode 4016 are electrically connected to a terminalincluded in the FPC 4324 through an anisotropic conductive film 4019.

The connection terminal electrode 4015 is formed using the sameconductive film as a first electrode layer 4030, and the terminalelectrode 4016 is formed using the same conductive film as each ofsource and drain electrode layers included in thin film transistors 4010and 4011.

Further, as illustrated in FIGS. 4A to 4C, the signal line drivercircuit 4323 formed using a single crystal semiconductor film or apolycrystalline semiconductor film over a separately prepared substrateis mounted by an FPC so as to be provided in the supporting portion4308. A variety of signals and potentials are supplied from the FPC 4324to the signal line driver circuit 4323, the scan line driver circuit4321 a, and the display portion 4301.

Note that there is no particular limitation on the connection method ofthe signal line driver circuit 4323: a COG method, a wire bondingmethod, a TAB method, or the like can be used.

The first display portion 4301 and the scan line driver circuit 4321 awhich are provided over the element substrate 4331 a each include aplurality of thin film transistors. In FIGS. 18A and 18B, FIG. 19, andFIG. 20, the thin film transistor 4010 included in the first displayportion 4301 and the thin film transistor 4011 included in the scan linedriver circuit 4321 a are illustrated. Over the thin film transistors4010 and 4011, insulating layers 4020 and 4021 are provided. Aninsulating film 4023 is an insulating film serving as a base film.

A variety of thin film transistors can be applied to the thin filmtransistors 4010 and 4011 without particular limitation. FIGS. 18A and18B, FIG. 19, and FIG. 20 each illustrate an example in whichinverted-staggered thin film transistors having a bottom-gate structureare used as the thin film transistors 4010 and 4011. Although the thinfilm transistors 4010 and 4011 are channel-etched thin film transistorsin the drawings, a channel-protective inverted-staggered thin filmtransistor in which a channel protective film is provided over asemiconductor layer may be used.

The thin film transistor 4010 included in the first display portion 4301is electrically connected to a display element to form a display panel.A variety of display elements can be used as the display element as longas display can be performed.

As a display panel, an electronic paper can be used. As for imagewriting methods of the electronic paper, there are many types dependingon a change of shape or position, a physical change, and the like of adisplay medium by an electric field, a magnetic field, light, heat, andthe like. For example, there are a twist ball-type, an electrophoresistype, a powder system type (also called a toner display), a liquidcrystal type, and the like.

FIGS. 18A and 18B and FIG. 22 illustrate examples of the case where anactive-matrix electronic paper is used as the first display panel 4311.An electronic papers have advantages such as readability which is ashigh as that of paper media, low power consumption compared to otherdisplay panels, and thin light form.

FIGS. 18A and 18B and FIG. 22 illustrate active-matrix electronic papersas examples of the display panel.

The electronic paper in FIG. 18A is an example of a display device usinga twist ball display method. The twist ball display method refers to amethod in which spherical particles each colored in black and white arearranged between electrode layers included in a display element, and apotential difference is generated between the electrode layers tocontrol the orientation of the spherical particles, so that display isperformed.

Between the first electrode layer 4030 connected to the thin filmtransistor 4010 and a second electrode layer 4031 provided for thesealing substrate 4332 a, spherical particles 4613 each of whichincludes a black region 4615 a, a white region 4615 b, and a cavity 4612which is filled with liquid around the black region 4615 a and the whiteregion 4615 b, are provided. A space around the spherical particles 4613is filled with a filler 4614 such as a resin. The second electrode layer4031 corresponds to a common electrode (counter electrode). The secondelectrode layer 4031 is electrically connected to a common potentialline.

Instead of the twist ball, an electrophoretic element can be used. Anexample of the case where an electrophoretic element is used as adisplay element is illustrated in FIG. 18B. Microcapsules 4713 eachhaving a diameter of about 10 μm to 200 μm, in which transparent liquid4712, negatively charged black microparticles 4715 a as first particles,and positively charged white microparticles 4715 b as second particlesare encapsulated, are used.

In the microcapsules 4713 provided between the first electrode layer4030 and the second electrode layer 4031, when an electric field isapplied by the first electrode layer 4030 and the second electrode layer4031, the white microparticles 4715 b and the black microparticles 4715a move to opposite directions to each other, so that white or black canbe displayed. A display element using this principle is anelectrophoretic display element. The electrophoretic display element hashigh reflectivity, and thus, an auxiliary light is not needed, powerconsumption is low, and a display portion can be recognized in a dimplace. In addition, even when power is not supplied to the displayportion, an image which has been displayed once can be maintained.Accordingly, a displayed image can be stored even when the display panelis distanced from an electric wave source.

Note that the first particle and the second particle each containpigment and do not move without an electric field. Moreover, the colorsof the first particle and the second particle are different from eachother (the particles may be colorless).

A solution in which the above microcapsules are dispersed in a solventis referred to as electronic ink. This electronic ink can be printed ona surface of glass, plastic, cloth, paper, or the like. Further, the useof a color filter or particles that have a pigment makes it possible toperform color display.

Note that the first particles and the second particles in themicrocapsules may be formed using a single material selected from aconductive material, an insulating material, a semiconductor material, amagnetic material, a liquid crystal material, a ferroelectric material,an electroluminescent material, an electrochromic material, and amagnetophoretic material, or a composite material of any of these.

Electronic Liquid Powder (registered trademark) can be used for anelectronic paper using liquid powders. An example of the case where anelectronic liquid powder is used as the display element is illustratedin FIG. 22. Positively charged black liquid powders 4815 a andnegatively charged white liquid powders 4815 b are contained in a space4812 segmented by the first electrode layer 4030, the second electrodelayer 4031, and a rib 4814. The space 4812 is filled with air.

When an electric field is applied by the first electrode layer 4030 andthe second electrode layer 4031, the black liquid powders 4815 a and thewhite liquid powders 4815 b move in opposite directions to display whiteor black. As the liquid powders, color powders of red, yellow, and/orblue may be used.

A light-emitting element using electroluminescence (an EL element) maybe used as the display element. Light-emitting elements usingelectroluminescence are classified according to whether a light-emittingmaterial is an organic compound or an inorganic compound; in general,the former is called an organic EL element, and the latter is called aninorganic EL element.

In an organic EL element, by application of voltage to a light-emittingelement, electrons and holes are separately injected from a pair ofelectrodes into a layer containing a light-emitting organic compound,and thus current flows. The carriers (electrons and holes) arerecombined, and thus the light-emitting organic compound is excited.When the light-emitting organic compound returns to a ground state fromthe excited state, light is emitted. Owing to such a mechanism, thislight-emitting element is called a current-excitation light-emittingelement.

Inorganic EL elements are classified according to their elementstructures into a dispersion-type inorganic EL element and a thin-filminorganic EL element. A dispersion-type inorganic EL element includes alight-emitting layer in which particles of a light-emitting material aredispersed in a binder, and its light emission mechanism isdonor-acceptor recombination type light emission that uses a donor leveland an acceptor level. A thin-film inorganic EL element has a structurewhere a light-emitting layer is sandwiched between dielectric layers,which are further sandwiched between electrodes, and its light emissionmechanism is localized type light emission that uses inner-shellelectron transition of metal ions. Description is made here using anorganic EL element as a light-emitting element.

In order to extract light emitted from the light-emitting element, atleast one of an anode and a cathode may be transparent. A light-emittingelement can have a top emission structure in which light is extractedthrough the surface opposite to the substrate; a bottom emissionstructure in which light is extracted through the surface on thesubstrate side; or a dual emission structure in which light is extractedthrough the surface opposite to the substrate and the surface on thesubstrate side.

An example of the case where a light-emitting display panel (EL panel)is used as the first display panel 4311 is illustrated in FIG. 19. Alight-emitting element 4513 which is a display element is electricallyconnected to the thin film transistor 4010 provided in the displayportion 4301. A structure of the light-emitting element 4513 is notlimited to the stacked-layer structure including the first electrodelayer 4030, an electroluminescent layer 4511, and the second electrodelayer 4031, which is illustrated in FIG. 19. The structure of thelight-emitting element 4513 can be changed as appropriate depending on adirection in which light is extracted from the light-emitting element4513, or the like.

A partition wall 4510 is formed using an organic resin film, aninorganic insulating film, or organic polysiloxane. It is particularlypreferable that the partition wall 4510 be formed using a photosensitivematerial to have an opening portion over the first electrode layer 4030so that a sidewall of the opening portion is formed as a tilted surfacewith continuous curvature.

The electroluminescent layer 4511 may be formed using a single layer ora plurality of layers stacked.

A protective film may be formed over the second electrode layer 4031 andthe partition wall 4510 in order to prevent entry of oxygen, hydrogen,moisture, carbon dioxide, or the like into the light-emitting element4513. As the protective film, a silicon nitride film, a silicon nitrideoxide film, a DLC film, or the like can be formed. A filler 4514 isprovided in a space sealed with the element substrate 4331 a, thesealing substrate 4332 a, and the sealant 4005 so as to seal closely. Itis preferable that a panel be packaged (sealed) with a protective film(such as a laminate film or an ultraviolet curable resin film) or acover material with high air-tightness and little degasification so thatthe panel is not exposed to the outside air, in this manner.

As the filler 4514, an ultraviolet curable resin or a thermosettingresin can be used as well as an inert gas such as nitrogen or argon. Forexample, polyvinyl chloride (PVC), acrylic, polyimide, an epoxy resin, asilicone resin, polyvinyl butyral (PVB), or ethylene vinyl acetate (EVA)can be used. For example, nitrogen is used for the filler.

In addition, if needed, an optical film such as a polarizing plate, acircularly polarizing plate (including an elliptically polarizingplate), a retardation plate (a quarter-wave plate or a half-wave plate),or a color filter may be provided as appropriate on a light-emittingsurface of the light-emitting element. Further, the polarizing plate orthe circularly polarizing plate may be provided with an anti-reflectionfilm. For example, anti-glare treatment by which reflected light isdiffused by roughness on the surface so as to reduce the glare can beperformed.

An example of the case where a liquid crystal display panel is used asthe first display panel 4311 is illustrated in FIG. 20. In FIG. 20, aliquid crystal element 4013 which is a display element includes thefirst electrode layer 4030, the second electrode layer 4031, and aliquid crystal layer 4008. Insulating films 4032 and 4033 serving asorientation films are provided to hold the liquid crystal layer 4008therebetween. The second electrode layer 4031 is provided on the sealingsubstrate 4332 a side, and the first electrode layer 4030 and the secondelectrode layer 4031 are stacked with the liquid crystal layer 4008provided therebetween.

Reference numeral 4035 indicates a columnar spacer formed by selectivelyetching the insulating film. The columnar spacer 4035 is provided inorder to control the thickness of the liquid crystal layer 4008 (a cellgap). A spherical spacer may also be used.

Although not shown in the liquid crystal display device in FIG. 20, acolor filter (a coloring layer), a black matrix (a light-shieldinglayer), an optical member (an optical substrate) such as a polarizingmember, a retardation member, or an anti-reflection member, and the likeare provided as appropriate. For example, circular polarization by usinga polarizing substrate and a retardation substrate may be used. Abacklight, a side light, or the like may be used as a light source; asthe backlight, it is preferable to use an EL panel in the point of smallthickness.

Alternatively, liquid crystal exhibiting a blue phase for which analignment film is unnecessary may be used. A blue phase is one of liquidcrystal phases, which is generated just before a cholesteric phasechanges into an isotropic phase while temperature of cholesteric liquidcrystal is increased. Since the blue phase is generated within an onlynarrow range of temperature, liquid crystal composition containing achiral agent at 5 wt % or more so as to improve the temperature range isused for the liquid crystal layer 4008. Since the liquid crystalcomposition including a blue phase liquid crystal and a chiral agent hasa response time as short as 10 μs to 100 μs and is optically isotropic,orientation treatment is not necessary and viewing angle dependence issmall.

Although FIG. 20 illustrates an example of a light-transmissive liquidcrystal display panel, the present invention can also be applied to areflective liquid crystal display panel or a light-semi-transmissiveliquid crystal display panel.

In FIGS. 18A and 18B, FIG. 19, FIG. 20, and FIG. 22, a plastic havinglight-transmitting properties can be used as each of the elementsubstrate 4331 and the sealing substrate 4332. As the plastic, afiberglass-reinforced plastics (FRP) plate, a polyvinyl fluoride (PVF)film, a polyester film, or an acrylic resin film can be used. A sheetwith a structure in which an aluminum foil is sandwiched between PVFfilms or polyester films can be used.

The insulating layer 4020 serves as a protective film of a thin filmtransistor.

Note that the protective film is provided to prevent entry ofcontaminant impurities such as organic substance, metal, or moistureexisting in air and is preferably a dense film. The protective film maybe formed with a single layer or a stacked layer of a silicon oxidefilm, a silicon nitride film, a silicon oxynitride film, a siliconnitride oxide film, an aluminum oxide film, an aluminum nitride film,aluminum oxynitride film, and/or an aluminum nitride oxide film by asputtering method.

Further, the insulating layer 4021 serving as a planarization insulatingfilm is formed as the planarizing insulating film. The insulating layer4021 can be formed from an organic material having heat resistance, suchas polyimide, acrylic, benzocyclobutene, polyamide, or epoxy. Other thansuch organic materials, it is also possible to use a low-dielectricconstant material (a low-k material), a siloxane-based resin,phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), or thelike. The insulating layer may be formed by stacking a plurality ofinsulating films formed of these materials.

There is no particular limitation on the method of forming theinsulating layers 4020 and 4021. Any of the following methods can beused depending on the material of the insulating layer 4021: asputtering method, an SOG method, spin coating, dip coating, spraycoating, a droplet discharge method (e.g., an inkjet method, screenprinting, or offset printing), a doctor knife, a roll coater, a curtaincoater, a knife coater, or the like. In the case where the insulatinglayer is formed using a material solution, the semiconductor layer maybe annealed (at 200° C. to 400° C.) at the same time as a baking step.When the step of baking the insulating layers and the step of annealingthe semiconductor layer are performed at the same time, a display panelcan be manufactured efficiently.

The display panel displays an image by transmitting light from a lightsource or a display element. Therefore, the substrates and the thinfilms such as insulating films and conductive films provided for thedisplay portion where light is transmitted have light-transmittingproperties with respect to light in the visible-light wavelength range.

The first electrode layer 4030 and the second electrode layer 4031 (eachof which may be called a pixel electrode layer, a common electrodelayer, a counter electrode layer, or the like) for applying voltage tothe display element may have light-transmitting properties orlight-reflecting properties, depending on the direction in which lightis extracted, the position where the electrode layer is provided, thepattern structure of the electrode layer, and the like.

The first electrode layer 4030 and the second electrode layer 4031 canbe formed using a light-transmitting conductive material such as indiumoxide containing tungsten oxide, indium zinc oxide containing tungstenoxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, indium tin oxide (hereinafter referred to asITO), indium zinc oxide, or indium tin oxide to which silicon oxide isadded.

The first electrode layer 4030 and the second electrode layer 4031 eachcan be formed using one kind or plural kinds selected from metal such astungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium(V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co), nickel(Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), orsilver (Ag); an alloy thereof; and a nitride thereof.

A conductive composition containing a conductive high molecule (alsoreferred to as a conductive polymer) can be used for the first electrodelayer 4030 and the second electrode layer 4031. As the conductive highmolecule, a so-called π-electron conjugated conductive polymer can beused. For example, polyaniline or a derivative thereof, polypyrrole or aderivative thereof, polythiophene or a derivative thereof, a copolymerof two or more kinds of them, and the like can be given.

Since the thin film transistor is easily broken due to staticelectricity or the like, a protective circuit for protecting the drivercircuit is preferably provided over the same substrate for a gate lineor a source line. The protective circuit is preferably formed using anonlinear element.

Embodiment 5 can be implemented by being combined with any of thestructures described in the other embodiments as appropriate.

Embodiment 6

In Embodiment 6, examples of a material used forming an e-book readerand an element structure will be specifically described.

Since a signal line driver circuit is provided in a binding portion, itdoes not particularly need to have flexibility. Accordingly, asemiconductor integrated circuit chip (IC) which is capable ofhigh-speed operation and in which a semiconductor substrate (asemiconductor wafer) is used is preferably used as the signal linedriver circuit. As the semiconductor substrate, a single crystalsemiconductor substrate or a polycrystalline semiconductor substrate canbe used, and a semiconductor wafer such as a silicon wafer or agermanium wafer or a compound semiconductor wafer of gallium arsenide,indium phosphide, or the like is used.

Alternatively, a substrate (an SOI substrate) having an SOI structure inwhich a single crystal semiconductor layer is provided on an insulatingsurface may be used for the signal line driver circuit. The SOIsubstrate can be formed by a separation by implanted oxygen (SIMOX)method or a Smart-Cut (registered trademark) method. In the SIMOXmethod, after oxygen ions are implanted into a single crystal siliconsubstrate to form an oxygen containing layer containing oxygen at agiven depth, heat treatment is performed to form an embedded insulatinglayer at a given depth from the surface of the single crystal siliconsubstrate, and a single crystal silicon layer is formed on the embeddedinsulating layer. In the Smart-Cut (registered trademark) method,hydrogen ions are implanted into an oxidized single crystal siliconsubstrate to form a hydrogen-containing layer in a portion at a depthcorresponding to a desired depth, the oxidized single crystal siliconsubstrate is attached to another semiconductor substrate (such as asingle crystalline silicon substrate having a silicon oxide film forattachment on its surface), and heat treatment is performed to separatethe single crystal silicon substrate at the hydrogen-containing layer,and stacked layers of the silicon oxide film and the single crystallinesilicon layer is formed on the semiconductor substrate.

As a semiconductor element provided in a circuit portion of the e-bookreader, not to mention a field-effect transistor, a memory element whichuses a semiconductor layer can be employed; accordingly, a semiconductorintegrated circuit having functions required for various applicationscan be provided.

There is no particular limitation on the method by which a scan linedriver circuit and a display portion are provided as long as the scanline driver circuit and the display portion are provided over a flexiblesubstrate. The scan line driver circuit and the display portion may beformed directly on a flexible substrate. Alternatively, the scan linedriver circuit and the display portion may be first formed on anotherformation substrate, and then only an element layer may be transferredfrom the formation substrate to a flexible substrate by a separationmethod. For example, the scan line driver circuit and the displayportion can be formed on a formation substrate in the same step andtransferred to a flexible substrate of a display panel. In that case,since the scan line driver circuit and the display portion are formed inthe same step, they are preferably formed with transistors having thesame structure and material, in which case a reduction in cost can berealized. Consequently, channel layers of transistors included in thescan line driver circuit and the display portion are formed using thesame material.

Alternatively, after transfer from a formation substrate to a flexiblesubstrate, attachment of components over the flexible substrate to asubstrate of a display panel may be performed. For example, a pluralityof scan line driver circuits are formed over a formation substrate andtransferred to a flexible supporting substrate, and then the pluralityof scan line driver circuits are separated into individual scan linedriver circuits with the flexible supporting substrate divided, and thescan line driver circuit provided over the flexible supporting substratemay be attached as many as needed to one display panel. In that case,since the scan line driver circuit and the display portion are formed indifferent steps, transistors having different structures and materialscan be used.

The above transfer method and direct formation method may be combined.For example, a wiring for electrically connecting a display portion, ascan line driver circuit, an FPC, and the like may be directly formed ona flexible substrate of a display panel by a printing method or thelike.

The formation substrate may be selected as appropriate depending on theformation process of the element layer. For example, a glass substrate,a quartz substrate, a sapphire substrate, a ceramic substrate, or ametal substrate having an insulating layer on its surface can be used asthe formation substrate. Alternatively, a plastic substrate having heatresistance to the processing temperature may be used.

For the flexible substrate, an aramid resin, a polyethylene naphthalate(PEN) resin, a polyether sulfone (PES) resin, a polyphenylene sulfide(PPS) resin, a polyimide (PI) resin, or the like can be used.Alternatively, a prepreg that is a structure body in which fiber isimpregnated with an organic resin may be used.

There is no particular limitation on the method of transferring theelement layer from the formation substrate to another substrate, and avariety of methods can be used. For example, a separation layer may beformed between the formation substrate and the element substrate.

Note that the element layer in this specification includes not only asemiconductor element layer provided on the element substrate side butalso a counter electrode layer or the like provided on the countersubstrate side. Accordingly, the separation step can be used for boththe element substrate and sealing substrate sides. Further, in view ofthe simplicity of the manufacturing process, after the element layer istransferred from the formation substrate to the flexible substrate, themanufacturing process can be performed with the flexible substratetemporally attached to a glass substrate or the like.

The separation layer is formed to have a single-layer structure or astacked-layer structure including a layer formed of an element such astungsten (W), molybdenum (Mo), titanium (Ti), tantalum (Ta), niobium(Nb), nickel (Ni), cobalt (Co), zirconium (Zr), zinc (Zn), ruthenium(Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), orsilicon (Si); or an alloy material or a compound material containing anyof the elements as its main component by a sputtering method, a plasmaCVD method, a coating method, a printing method, or the like. Acrystalline structure of a layer containing silicon may be any one of anamorphous structure, a microcrystalline structure, and a polycrystallinestructure. Note that a coating method includes a spin-coating method, adroplet discharge method, and a dispensing method in its category here.

In the case where the separation layer has a single-layer structure, itis preferable to form a tungsten layer, a molybdenum layer, or a layercontaining a mixture of tungsten and molybdenum. Alternatively, a layercontaining oxide or oxynitride of tungsten, a layer containing oxide oroxynitride of molybdenum, or a layer containing oxide or oxynitride of amixture of tungsten and molybdenum is formed. Note that the mixture oftungsten and molybdenum, for example, corresponds to an alloy oftungsten and molybdenum.

In the case where the separation layer has a stacked-layer structure, itis preferable to form, as a first layer, a tungsten layer, a molybdenumlayer, or a layer containing a mixture of tungsten and molybdenum, andform, as a second layer, oxide, nitride, oxynitride, or nitride oxide oftungsten, molybdenum, or a mixture of tungsten and molybdenum.

In the case where the separation layer is formed to have a stacked-layerstructure including a layer containing tungsten and a layer containingoxide of tungsten, the stacked-later structure may be formed byutilization of the following: a layer containing tungsten is formedfirst and an insulating layer formed of oxide is formed thereover toform a layer containing oxide of tungsten at the interface between thetungsten layer and the insulating layer. Furthermore, the surface of thelayer containing tungsten may be subjected to thermal oxidationtreatment, oxygen plasma treatment, or treatment using a strongoxidizing solution such as ozone water to form a layer containing oxideof tungsten. Plasma treatment or heat treatment may be performed in anatmosphere of oxygen, nitrogen, or dinitrogen monoxide alone, or a mixedgas of the above gas and another gas. The same applies to the case offorming a layer containing nitride, oxynitride, or nitride oxide oftungsten. After the layer containing tungsten is formed, a siliconnitride layer, a silicon oxynitride layer, or a silicon nitride oxidelayer may be formed thereover.

Note that for the step of transferring the element layer to anothersubstrate, any of the following methods can be used as appropriate: amethod in which a separation layer is formed between a substrate and anelement layer, a metal oxide film is provided between the separationlayer and the element layer, and the metal oxide film is embrittled bycrystallization, thereby separating the element layer; a method in whichan amorphous silicon film containing hydrogen is provided between asubstrate having high heat resistance and an element layer, and theamorphous silicon film is removed by laser light irradiation or etching,thereby separating the element layer; a method in which a separationlayer is formed between a substrate and an element layer, a metal oxidefilm is provided between the separation layer and the element layer, themetal oxide film is embrittled by crystallization, part of theseparation layer is removed by etching using a solution or a fluoridehalogen gas such as NF₃, BrF₃, or ClF₃, and then the element layer isseparated at the embrittled metal oxide film; a method in which asubstrate over which an element layer is formed is mechanically removedor is removed by etching using a solution or a fluoride halogen gas suchas NF₃, BrF₃, or ClF₃; and the like. Alternatively, a method may be usedin which a film containing nitrogen, oxygen, hydrogen, or the like(e.g., an amorphous silicon film containing hydrogen, an alloy filmcontaining hydrogen, or an alloy film containing oxygen) is used as aseparation layer, and the separation layer is irradiated with laserlight to release nitrogen, oxygen, or hydrogen contained in theseparation layer as a gas, thereby promoting separation between theelement layer and the substrate.

Combination of any of the above separation methods makes it easier toperform the transferring step. In other words, separation can also beperformed with physical force (e.g., by a machine or the like) aftermaking it easier for the separation layer and the element formationlayer to be separated by laser light irradiation, etching of theseparation layer with a gas, a solution, or the like, or mechanicalremoval of the separation layer with a sharp knife, scalpel, or thelike.

Alternatively, the interface between the separation layer and theelement layer may be soaked with a liquid to separate the element layerfrom the substrate. Water or the like can be used as the liquid.

There is no particular limitation on the kind of transistor included inthe e-book reader disclosed in this specification. Accordingly, avariety of structures and semiconductor materials can be used for thetransistor.

Examples of a structure of a thin film transistor is described withreference to FIGS. 21A to 21D. FIGS. 21A to 21D illustrates examples ofthe thin film transistor which can be applied to the thin filmtransistor 4010 in Embodiment 5.

In FIGS. 21A to 21D, the insulating film 4023 is formed over the elementsubstrate 4331 a, and thin film transistors 4010 a, 4010 b, 4010 c, and4010 d are provided over the insulating film 4023. The insulating layers4020 and 4021 are formed over each of the thin film transistors 4010 a,4010 b, 4010 c, and 4010 d, and the first electrode layer 4030 isprovided to be electrically connected to the thin film transistors 4010a, 4010 b, 4010 c, and 4010 d.

The thin film transistor 4010 a has another structure of the thin filmtransistor 4010 illustrated in FIGS. 18A and 18B, FIG. 19, and FIG. 20,in which wiring layers 405 a and 405 b serving as source and drainelectrode layers are in contact with a semiconductor layer 403 withoutn⁺ layers interposed therebetween.

The thin film transistor 4010 a is an inverted-staggered thin filmtransistor in which a gate electrode layer 401, a gate insulating layer402, the semiconductor layer 403, and the wiring layers 405 a and 405 bserving as source and drain electrode layers are provided over theelement substrate 4331 a having an insulating surface and the insulatingfilm 4023. The n⁺ layers 404 a and 404 b are semiconductor layers havinglower resistance than the semiconductor layer 403.

The thin film transistor 4010 b is a bottom-gate thin film transistor inwhich the gate electrode layer 401, the gate insulating layer 402, thewiring layers 405 a and 405 b serving as source and drain electrodelayers, n⁺ layers 404 a and 404 b serving as source and drain regions,and the semiconductor layer 403 are provided over the element substrate4331 a having an insulating surface and the insulating film 4023. Inaddition, the insulating layer 4020 is provided in contact with thesemiconductor layer 403 so as to cover the thin film transistor 4010 b.

Note that the n⁺ layers 404 a and 404 b may be provided between the gateinsulating layer 402 and the wiring layers 405 a and 405 b.Alternatively, the n⁺ layers may be provided both between the gateinsulating layer and the wiring layers and between the wiring layers andthe semiconductor layer.

The gate insulating layer 402 exists in the entire region including thethin film transistor 4010 b, and the gate electrode layer 401 isprovided between the gate insulating layer 402 and the element substrate4331 a having an insulating surface. The wiring layers 405 a and 405 band the n⁺ layers 404 a and 404 b are provided over the gate insulatinglayer 402. In addition, the semiconductor layer 403 is provided over thegate insulating layer 402, the wiring layers 405 a and 405 b, and the n⁺layers 404 a and 404 b. Although not illustrated, a wiring layer isprovided over the gate insulating layer 402 in addition to the wiringlayers 405 a and 405 b, and the wiring layer extends beyond theperimeter of the semiconductor layer 403.

The thin film transistor 4010 c has another structure of the thin filmtransistor 4010 b, in which source and drain electrode layers are incontact with a semiconductor layer without n⁺ layers interposedtherebetween.

The gate insulating layer 402 exists in the entire region including thethin film transistor 4010 c, and the gate electrode layer 401 isprovided between the gate insulating layer 402 and the element substrate4331 a having an insulating surface. The wiring layers 405 a and 405 bare provided over the gate insulating layer 402. In addition, thesemiconductor layer 403 is provided over the gate insulating layer 402and the wiring layers 405 a and 405 b. Although not illustrated, awiring layer is provided over the gate insulating layer 402 in additionto the wiring layers 405 a and 405 b, and the wiring layer extendsbeyond the perimeter of the semiconductor layer 403.

The thin film transistor 4010 d is a top-gate thin film transistor andan example of a planar thin film transistor. The semiconductor layer 403including the n⁺ layers 404 a and 404 b serving as source and drainregions is formed over the element substrate 4331 a having an insulatingsurface and the insulating film 4023. The gate insulating layer 402 isformed over the semiconductor layer 403, and the gate electrode layer401 is formed over the gate insulating layer 402. In addition, thewiring layers 405 a and 405 b serving as source and drain electrodelayers are formed in contact with the n⁺ layers 404 a and 404 b. The n⁺layers 404 a and 404 b are semiconductor layers having lower resistancethan the semiconductor layer 403.

The thin film transistor may be a top-gate forward-staggered thin filmtransistor.

Although a single-gate transistor is described in this embodiment, amulti-gate transistor such as a double-gate transistor may be used. Inthat case, a gate electrode layer may be provided above and below thesemiconductor layer, or a plurality of gate electrode layers may beprovided only on one side of (above or below) the semiconductor layer.

There is no particular limitation on the semiconductor material used forthe semiconductor layer. Examples of the material used for thesemiconductor layer of the thin film transistor are described below.

As a material for the semiconductor layer included in the semiconductorelement, it is possible to use an amorphous semiconductor (hereinafter,also referred to as “AS”) that is formed by a sputtering method or avapor-phase growth method using a semiconductor material gas typified bysilane or germane, a polycrystalline semiconductor that is obtained bycrystallizing the amorphous semiconductor by utilizing light energy orthermal energy, a microcrystalline semiconductor (also referred to as asemi-amorphous or microcrystal semiconductor, and hereinafter, alsoreferred to as “SAS”), or the like. The semiconductor layer can bedeposited by a sputtering method, an LPCVD method, a plasma CVD method,or the like.

Considering Gibbs free energy, the microcrystalline semiconductor filmis in a metastable state intermediate between an amorphous state and asingle crystal state. In other words, the microcrystalline semiconductoris in a third state that is stable in free energy and has short-rangeorder and lattice distortion. Columnar-like or needle-like crystals growin the normal direction to the surface of the substrate. The Ramanspectrum of microcrystalline silicon, which is a typical example of amicrocrystalline semiconductor, is located in lower wave numbers than520 cm⁻¹ that represents the peak of the Raman spectrum of singlecrystal silicon. In other words, the peak of the Raman spectrum of themicrocrystalline silicon exists between 520 cm⁻¹ that represents that ofsingle crystal silicon and 480 cm⁻¹ that represents that of amorphoussilicon. In addition, the microcrystalline silicon contains hydrogen orhalogen of at least 1 atomic % or more in order to terminate a danglingbond. Moreover, the microcrystalline silicon contains a rare gas elementsuch as helium, argon, krypton, or neon to further promote latticedistortion, whereby a favorable microcrystalline semiconductor film withimproved stability can be obtained.

This microcrystalline semiconductor film can be formed by ahigh-frequency plasma CVD method with a frequency of several tens ofmegahertz to several hundreds of megahertz, or a microwave plasma CVDapparatus with a frequency of 1 GHz or more. Typically, themicrocrystalline semiconductor film can be formed with silicon hydridesuch as SiH₄, Si₂H₆, SiH₂Cl₂, or SiHCl₃, or SiCl₄ or SiF₄, and hydrogenwhich is for dilution. Alternatively, the microcrystalline semiconductorfilm can be formed with, in addition to silicon hydride and hydrogen,one or more kinds of rare gas elements selected from helium, argon,krypton, and neon for dilution. In such a case, the flow rate ratio ofhydrogen to silicon hydride is set to 5:1 to 200:1, preferably, 50:1 to150:1, and more preferably, 100:1.

Hydrogenated amorphous silicon is given as a typical example of anamorphous semiconductor, and polysilicon and the like is given as atypical example of a crystalline semiconductor. Polysilicon(polycrystalline silicon) includes so-called high-temperaturepolysilicon that contains, as its main component, polysilicon formed ata process temperature of 800° C. or higher, so-called low-temperaturepolysilicon that contains, as its main component, polysilicon formed ata process temperature of 600° C. or lower, and polysilicon formed bycrystallizing amorphous silicon by using an element which promotescrystallization, or the like. Needless to say, a microcrystallinesemiconductor or a semiconductor partially including a crystalline phasecan also be used as described above.

As the semiconductor material, a compound semiconductor such as GaAs,InP, SiC, ZnSe, GaN, or SiGe can be used as well as silicon (Si) orgermanium (Ge) alone.

In the case of using a crystalline semiconductor film for thesemiconductor layer, the crystalline semiconductor film may be formed byany of a variety of methods (e.g., laser crystallization, thermalcrystallization, or thermal crystallization using an element such asnickel which promotes crystallization). Further, when a microcrystallinesemiconductor that is SAS is crystallized by laser light irradiation,crystallinity thereof can be enhanced. In the case where an elementwhich promotes crystallization is not introduced, before beingirradiated with laser light, an amorphous silicon film is heated at 500°C. for one hour in a nitrogen atmosphere, whereby hydrogen contained inthe amorphous silicon film is released to a concentration of 1×10²⁰atoms/cm³ or less. This is because, if the amorphous silicon filmcontains a large amount of hydrogen, the amorphous silicon film would bedestroyed by laser light irradiation.

There is no particular limitation on the method of introducing a metalelement into the amorphous semiconductor film as long as the metalelement can exist on the surface of or inside the amorphoussemiconductor film. For example, a sputtering method, a CVD method, aplasma treatment method (e.g., a plasma CVD method), an adsorptionmethod, or a method of applying a metal salt solution can be used. Amongthe methods given above, the method using a solution is useful in termsof easy adjustment of the concentration of the metal element. At thistime, an oxide film is preferably deposited by UV light irradiation inan oxygen atmosphere, thermal oxidation, treatment with ozone water orhydrogen peroxide including a hydroxyl radical, or the like in order toimprove the wettability of the surface of the amorphous semiconductorfilm and to spread an aqueous solution on the entire surface of theamorphous semiconductor film.

In a crystallization step for crystallizing the amorphous semiconductorfilm to form a crystalline semiconductor film, an element which promotescrystallization (also referred to as a catalytic element or a metalelement) may be added to the amorphous semiconductor film, andcrystallization may be performed by heat treatment (at 550° C. to 750°C. for 3 minutes to 24 hours). As the element which promotes(accelerates) the crystallization, one or more of iron (Fe), nickel(Ni), cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium(Os), iridium (Ir), platinum (Pt), copper (Cu), and gold (Au) can beused.

In order to remove or reduce the element which promotes crystallizationfrom the crystalline semiconductor film, a semiconductor film containingan impurity element is formed in contact with the crystallinesemiconductor film so as to function as a gettering sink. As theimpurity element, an impurity element imparting n-type conductivity, animpurity element imparting p-type conductivity, a rare gas element, orthe like can be used. For example, it is possible to use one or morekinds of elements selected from phosphorus (P), nitrogen (N), arsenic(As), antimony (Sb), bismuth (Bi), boron (B), helium (He), neon (Ne),argon (Ar), krypton (Kr), and xenon (Xe). A semiconductor filmcontaining a rare gas element is formed in contact with the crystallinesemiconductor film containing the element which promotescrystallization, and then heat treatment is performed (at 550° C. to750° C. for 3 minutes to 24 hours). The element promotingcrystallization that is contained in the crystalline semiconductor filmmoves into the semiconductor film containing a rare gas element, andthus the element promoting crystallization which is contained in thecrystalline semiconductor film is removed or reduced. After that, thesemiconductor film containing a rare gas element, which has functionedas a gettering sink, is removed.

The amorphous semiconductor film may be crystallized by a combination ofthermal treatment and laser light irradiation. Alternatively, eitherthermal treatment or laser light irradiation may be performed pluraltimes.

A crystalline semiconductor film can also be formed directly over thesubstrate by a plasma method. A crystalline semiconductor film may beselectively formed over the substrate by a plasma method.

An oxide semiconductor may be used for the semiconductor layer. Forexample, zinc oxide (ZnO), tin oxide (SnO₂), or the like can be used. Inthe case of using ZnO for the semiconductor layer, Y₂O₃, Al₂O₃, or TiO₂,a stacked layer thereof, or the like can be used for a gate insulatinglayer, and ITO, Au, Ti, or the like can be used for a gate electrodelayer, a source electrode layer, and a drain electrode layer. Inaddition, In, Ga, or the like may be added to ZnO.

As the oxide semiconductor, a thin film represented by InMO₃ (ZnO)_(m)(m>0) can be used. Note that M denotes one or more of metal elementsselected from gallium (Ga), iron (Fe), nickel (Ni), manganese (Mn), andcobalt (Co). For example, M is gallium (Ga) in some cases, and in othercases, M contains other metal elements in addition to Ga, such as Ga andNi or Ga and Fe. Furthermore, the above oxide semiconductor may containa transition metal element such as Fe or Ni or an oxide of thetransition metal as an impurity element in addition to a metal elementcontained as M. For example, an In—Ga—Zn—O-based non-single-crystal filmcan be used as the oxide semiconductor layer.

As the oxide semiconductor layer (the InMO₃(ZnO)_(m) (m>0) film), anInMO₃(ZnO)_(m) film (m>0) in which M is another metal element may beused instead of the In—Ga—Zn—O-based non-single-crystal film. As theoxide semiconductor which is applied to the oxide semiconductor layer,any of the following oxide semiconductors can be applied in addition tothe above: an In—Sn—Zn—O based oxide semiconductor; an In—Al—Zn—O basedoxide semiconductor; a Sn—Ga—Zn—O based oxide semiconductor; anAl—Ga—Zn—O based oxide semiconductor; a Sn—Al—Zn—O based oxidesemiconductor; an In—Zn—O based oxide semiconductor; a Sn—Zn—O basedoxide semiconductor; an Al—Zn—O based oxide semiconductor; an In—O basedoxide semiconductor; a Sn—O based oxide semiconductor; and a Zn—O basedoxide semiconductor.

Embodiment 6 can be implemented by being combined with any of thestructures described in the other embodiments as appropriate.

This application is based on Japanese Patent Application serial no.2009-112375 filed with Japan Patent Office on May 2, 2009, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. (canceled)
 2. A display device comprising: afirst display panel having flexibility comprising a first displayportion and a second display portion provided on a rear side of thefirst display panel; a binding portion provided at an edge of the firstdisplay panel, wherein the binding portion has a hollow; and a signalline driver circuit provided inside the binding portion.
 3. The displaydevice according to claim 2, comprising: a flexible printed circuitinside the binding portion; and an integrated circuit chip comprisingthe signal line driver circuit on the flexible printed circuit andinside the binding portion.
 4. The display device according to claim 2,comprising: an integrated circuit chip comprising the signal line drivercircuit on the first display panel and inside the binding portion. 5.The display device according to claim 2, comprising: a printed boardinside and attached to the binding portion; and an integrated circuitchip comprising the signal line driver circuit on the printed board andinside the binding portion.
 6. The display device according to claim 2,comprising: a second display panel having flexibility on a side of thefirst display portion; and a third display panel having flexibility on aside of the second display portion, wherein the binding portion isprovided at an edge of the second display panel and an edge of the thirddisplay panel.
 7. A display device comprising: a first display panelhaving flexibility comprising a first display portion and a seconddisplay portion provided on a rear side of the first display panel; abinding portion provided at an edge of the first display panel, whereinthe binding portion has a hollow; and a signal line driver circuitprovided inside the binding portion, wherein: the first display panelcomprises a first substrate having a light-transmitting property, asecond substrate having a light-transmitting property, and a displayelement between the first substrate and the second substrate; the firstdisplay portion is provided on a first substrate side; and the seconddisplay portion is provided on a second substrate side.
 8. The displaydevice according to claim 7, wherein the display element is anelectroluminescence element.
 9. The display device according to claim 7,comprising: a flexible printed circuit inside the binding portion; andan integrated circuit chip comprising the signal line driver circuit onthe flexible printed circuit and inside the binding portion.
 10. Thedisplay device according to claim 7, comprising: an integrated circuitchip comprising the signal line driver circuit on the first displaypanel and inside the binding portion.
 11. The display device accordingto claim 7, comprising: a printed board inside and attached to thebinding portion; and an integrated circuit chip comprising the signalline driver circuit on the printed board and inside the binding portion.12. The display device according to claim 7, comprising: a seconddisplay panel having flexibility on a side of the first display portion;and a third display panel having flexibility on a side of the seconddisplay portion, wherein the binding portion is provided at an edge ofthe second display panel and an edge of the third display panel.
 13. Adisplay device comprising: a first display panel having flexibilitycomprising a first display portion and a second display portion providedon a rear side of the first display panel; a binding portion provided atan edge of the first display panel, wherein the binding portion has ahollow; a signal line driver circuit provided inside the bindingportion; wherein: the first display panel comprises a first substratehaving a light-transmitting property, a second substrate having alight-transmitting property, and a first display element and a seconddisplay element between the first substrate and the second substrate;the first display portion is provided on a first substrate side; thesecond display portion is provided on a second substrate side; the firstdisplay element is configured to perform display on the first displayportion; and the second display portion is configured to perform displayon the second display portion.
 14. The display device according to claim13, wherein the first display element and the second display element areeach an electroluminescence element.
 15. The display device according toclaim 13, comprising: a flexible printed circuit inside the bindingportion; and an integrated circuit chip comprising the signal linedriver circuit on the flexible printed circuit and inside the bindingportion.
 16. The display device according to claim 13, comprising: anintegrated circuit chip comprising the signal line driver circuit on thefirst display panel and inside the binding portion.
 17. The displaydevice according to claim 13, comprising: a printed board inside andattached to the binding portion; and an integrated circuit chipcomprising the signal line driver circuit on the printed board andinside the binding portion.
 18. The display device according to claim13, comprising: a second display panel having flexibility on a side ofthe first display portion; and a third display panel having flexibilityon a side of the second display portion, wherein the binding portion isprovided at an edge of the second display panel and an edge of the thirddisplay panel.